Chem 1411 Test 2

What is molarity? How is it useful?

Molarity is a way of expressing solution concentration as the number of moles of solute per liter of solution. (mol solute /L solution). It's useful because it can be used to convert between moles of solute and liters of solution.

What is the de Broglie wavelength of an electron? What determines the value of the de Broglie wavelength for an electron?

The De Broglie relation is an observation that the wavelength of a particle is inversely proportional to its momentum. The speed of the electron determines the value of the De Broglie wavelength.

What are oxidation states?

The oxidation state or oxidation number is a number given to each atom based on the electron assignments. It is the charge an atom would have if all shared electrons were assigned to the atom with a greater attraction for those electrons.

What is the SI unit of energy? List some other common units of energy.

kg x m2/s2 called Joule •kJ, Calorie and kilowatt-hour

State function? Example.

-A state function is a mathematical function whose result depends only on the initial and final conditions, not on the process used. Examples are pressure, volume, and internal energy. Ex. To reach the top of the mountain there are two trails: A. Long and winding B. Short but steep Regardless of the trail, when you reach the top, you will be 10,000 feet above the base. The distance from the base to the peak of the mountain is a state function. It depends only on the difference in elevation between the base and the peak, not on how you arrive there!

What are the basic postulates of kinetic molecular theory? How does the concept of pressure follow from kinetic molecular theory?

1) size of particle negligibly small 2) average KE is proportional to temperature in K 3) collision of one particle with another is completely elastic •P= F/area•according to kinetic molecular theory, gas is collection of particles in constant motion •as particle collides, it exerts force •result of many forces is a constant pressure

What are the common units of pressure? List them in order of smallest to largest unit.

101,325 Pa = 760 torr = 760 mmHg = 29.92 in Hg = 14.7 psi = 1 atm

Make sketches of the general shapes of the s, p, and d orbitals.

1s = circular cloud Px,Py,Pz are the bowtie shape on the different axises. D orbitals are pretty complicated.

What does it mean for a compound to be soluble? Insoluble?

A compound is soluble if it dissolves in water. A compound is insoluble if it doesn't dissolve in water.

What is a gas-evolution reaction? Give an example.

A gas-evolution reaction is an aqueous reaction that forms a gas when two substances are mixed. Example: H₂SO₄(aq) + CaCO₃ → CO₂(g) + H₂O(l) + CaSO₄(aq)

What is a manometer? How does it measure the pressure of a sample of gas?

A manometer is a U-shaped tube containing dense liquid, usually mercury. In an open-ended manometer, one end of the tube is open to atmospheric pressure and the other is attached to a flask containing the gas sample. If the pressure of the gas sample is exactly equal to atmospheric pressure, the mercury levels on both sides of the tube are the same. If the pressure of the sample is greater than atmospheric pressure, the mercury level on the sample side of the tube is lower than on the side open to the atmosphere. If the pressure of the sample is less than atmospheric pressure, the mercury level on the sample side is higher than on the side open to the atmosphere. This type of manometer always measures the pressure of the gas sample relative to the atmospheric pressure. The difference in height between the two levels is equal to the pressure difference from atmospheric pressure. •The pressure of a gas trapped in a container can be measured with an instrument called a manometer. •Manometers are U-shaped tubes partially filled with a liquid that is connected to the gas sample on one side and open to the air on the other. •A competition is established between the pressures of the atmosphere and the gas. •The difference in the liquid levels is a measure of the difference in pressure between the gas and the atmosphere.

Explain how a molecular equation, a complete ionic equation, and a net ionic equation differ.

A molecular equation shows the complete neutral formulas for each compound as if they existed as molecules. A complete ionic equation lists individually all the ions present as either reactants or products in a chemical reaction, and a net ionic equation excludes the spectator ions that don't change during the reaction.

What is a photon? How is the energy of a photon related to its wavelength? Its frequency?

A photon is the smallest possible packet of electromagnetic radiation with an energy equal to hv. Therefore, frequency is directly proportional to energy of a photon and wavelength is inversely proportional to the energy of a photon.

What is a probability distribution map?

A probability distribution map is a statistical map that shows where an electron is likely to be found under a given set of conditions.

What is an aqueous solution? What is the difference between the solute and the solvent?

A solution in which water is the solvent is an aqueous solution. The majority component is the solvent. The minority component is the solute. The solvent dissolves the solute. If the attractions between solute and solvent are strong enough, the solute will dissolve.

Explain the difference between a strong acid and a weak acid.

A strong acid completely ionizes in water, while a weak acid doesn't completely ionize in water. A solution of a weak acid is composed mostly of the nonionized acid.

Explain how a strong electrolyte, a weak electrolyte, and a nonelectrolyte differ.

A strong electrolyte is a substance that completely dissociates into ions when dissolved in water and conducts electricity easily. A weak electrolyte is a substance that does not dissociate completely in water and conduct electricity weakly. A nonelectrolyte is a compound that does not dissociate into ions in water and do not conduct electricity. Strong electrolytes are materials that dissolve completely as ions. -Ionic compounds and strong acids. -Solutions are good conductors of electricity. Weak electrolytes are materials that dissolve mostly as molecules but partially as ions. -Weak acids. -Solutions conduct electricity, but not well.

In a redox reaction, which reactant is the oxidizing agent? The reducing agent?

A substance that causes the oxidation of another substance is called an oxidizing agent. A substance that causes the reduction of another substance is called a reducing agent.

What is trajectory? What kind of information do you need to predict the trajectory of a particle?

A trajectory is a path that is determined by a particle's velocity, its position, and the forces acting on it. In classical mechanics, both the position and velocity are required to predict a trajectory.

Define the wavelength and amplitude of a wave. How are these related to the energy of the wave?

A wavelength is the distance between adjacent crests of a wave. An amplitude is the vertical height of a crest of a wave, which is a measure of wave intensity. Amplitude is directly proportional to the energy of a wave, whereas the wavelength is inversely proportional to the energy of a wave.

List all the orbitals in each principal level. Specify the three quantum numbers for each orbital. a.n=1 b.n=2 c. n=3 d.n=4

A) n=1 l= 0 ml = 0 B) n =2 l=0,1 ml = -1,0,1 C)n=3 l= 0,1,2 ml = -2,-1,0,1,2 D)n=4 l=0,1,2,3 ml=-3,-2,-1,0,1,2,3

Give an approximate range of wavelengths for each type of electromagnetic radiation/summarize the characteristics and/or the uses of each. a. gamma rays b. X-rays c. UV rays d. Visible Light e. Infrared Radiation f. Microwave Radiation g. Radio Waves

A. Range: 10^-11 - 10^-15 m; produced by sun , other stars; human exposure=dangerous, can damage biological molecules B. Range: 10^-8 - 10^-11 m; used in medicine; can pass thru many objects; Excessive exposure can cause cancer C. Range: .4x10^-6 - 10^-8 m; component of sun light(sunburn); Excessive exposure can cause skin cancer, premature wrinkling,cataracts D. Range: .75x10^-6 - .4x10-6 m;will not damage molecules;molecules change its shape and make vision E. Range: .75x10^-6 - 10^-3 m; heat feel from hot object; not visible by eye (use night vision) F.Range: 10^-3 - 10^-1 m; used in radar and microwaves; absorbs by water and heat substances G. Range: 10^-1 - 10^5 m; used for AM + FM radio, phones, etc

Explain how the sum of heat and work can be a state function, even though heat and work are themselves not state functions.

According to the first law of thermodynamics, the change in the internal energy of the system (ΔE) must be the sum of the heat transferred (q) and the workd done (w): ΔE=q+w. The total change in internal energy (ΔE) is the difference between its initial energy and its final energy. The amount of the work done and the amount of heat transferred is dependent on the details of the path. In one path, more energy may be transferred through conversion to heat energy (if, for example, there is more friction). In another path, more energy may be transferred through work. Work and heat are not state functions, but their sum (ΔE) is constant.

What is an acid-base reaction? Give an example.

Acid-base reaction: -Also called a neutralization reaction -An acid reacts with a base, and the two neutralize each other, producing water (or in some cases a weak electrolyte). When an acid and base are mixed, the H⁺(aq) from the acid and the OH⁻(aq) from the base combine to form H₂O(l). Example: HCl(aq) + NaOH(aq) → H₂O(l) + NaCl(aq)

What is the Arrhenius definition of an acid? A base?

Acid: a substance that produces H⁺ ions in aqueous solution. Base: a substance that produces OH⁻ ions in aqueous solution.

What is an emission spectrum? How does an emission spectrum of a gas in a discharge tube differ from a white light spectrum?

An emission spectrum is the range of wavelengths emitted by a particular element and is used to identify the element. The white light spectrum is continuous, meaning that there are no sudden interruptions in the intensity of the light as a function of wavelength. The spectrum consists of all wavelengths. Emission spectra are not continuous. They consist of bright lines at specific wavelengths, with complete darkness in between.

Explain the difference between an exothermic and an endothermic reaction. Give the sign of ΔH for each type of reaction.

An endothermic reaction has a positive ΔH and absorbs heat from the surroundings. An endothermic reaction feels cold to the touch. An exothermic reaction has a negative ΔH and gives off heat to the surroundings. An exothermic reaction feels warm to the touch.

What is a quantum-mechanical orbital?

An orbital is a probability distribution map showing where the electron is likely to be found.

What is a precipitation reaction? Give an example.

Are ones in which a solid forms when we mix two solutions. -Reactions between aqueous solutions of ionic compounds produce an ionic compound that is insoluble in water. The insoluble product is called a precipitate. Example: 2KI(aq) + Pb(NO₃)₂(aq) →PbI₂(s) + 2KNO₃(aq)

Why are atoms usually portrayed as spheres when most orbitals are not spherically shaped?

Atoms are usually drawn as spheres because most atoms contain many electrons occupying a number of different orbitals. Therefore, the shape of an atom is obtained by superimposing all of its orbitals. If the s,p, and d orbitals are superimposed, they have a spherical shape.

Explain how the high specific heat capacity of water can affect the weather in coastal regions.

Because water has such a high heat capacity, it can moderate temperature changes. This keeps coastal temperatures more constant. Changing the temperature of water absorbs or releases large quantities of energy for a relatively small change in temperature. This serves to keep the air temperature of coastal areas more constant than the air temperature in inland areas.

Deviations from the ideal gas law are often seen at high pressure and low temperature. Explain this in light of kinetic molecular theory.

Behave ideally when: 1) V is small compared to space 2) forces between particles not significant •high pressure, number molecules increases, V greater, interactions more significant •low temperature, not moving as fast, greater opportunity to interact

Summarize each of the simple gas laws (Boyle's law, Charles's law, and Avogadro's law). For each law, explain explain the relationship between the two variables and also state which variables must be kept constant.

Boyle's law states that the volume of the gas varies inversely to the pressure on the gas, while temperature and number of moles are kept constant (P1V1 = P2V2). Charles's law states that the volume of a gas is directly proportional to the temperature of the gas, while pressure and number of moles are kept constant (V1/T1 = V2/T2). All temperatures must be in kelvins when used in gas law calculations. Avogadro's law states that the volume of a gas is directly proportional to the number of moles of the gas, while pressure and temperature are kept constant (V1/n1 = V2/n2).

Explain how Boyle's Law, Charle's Law, Avogadro's Law and Dalton's law all follow from kinetic molecular theory.

Boyles Law: •constant number particles at constant temp, volume inversely proportional to pressure •decrease V, force gas to occupy smaller space •as long of temp the same, result is greater number of collisions, and greater pressure Charle's Law: •constant number of particles, constant P, volume directly proportional to temp•increase T, average speed and KE increases •more frequent collisions= more pressure •only way for P to stay constant is for V to increase Avogadro's Law: •constant temp and P, volume of gas proportional to number of particles •increase number particles, number collisions increases •only way for P to stay constant is for volume to increase Dalton's Law: •total P is sum of partial pressures •gases act identically to but independently of each other •particles have negligible size and do not interact •mass distinguishes particles, but all have same average KE

What are complementary properties? How does electron diffraction demonstrate the complementarity of the wave nature and particle nature of the electron?

Complementary properties are those properties that exclude one another, i.e., the more you know about one, the less you know about the other. For example, the wave nature and particle nature of the electron are complementary. Which of the two complementary properties you observe depends on on the experiment you perform. In electron diffraction, when you try to observe which hole the electron goes through, you lose the interference pattern. When you try to observe the interference pattern, you cannot determine which hole the electron goes through.

What are the cations and anions whose compounds are usually soluble? What are the exceptions? What are the anions whose compounds are mostly insoluble? What are the exceptions?

Compounds Containing the Following Ions Are Generally Soluble Exceptions L i +, N a +, K +, and N H 4 + None N O 3 − and C 2 H 3 O 2 − None C l −, B r −, and I − When these ions pair with A g +, H g 4 2+ or P b2+ the resulting compounds are insoluble. S O 4 2− When S O 4 2− pairs with Sr2+, Ba2+, Pb2+, Ag+, or Ca2+, the resulting compound is insoluble. Compounds Containing the Following Ions Are Generally Insoluble Exceptions O H − and S 2− When these ions pair with L i +, N a +, K +, or N H 4 +, the resulting compounds are soluble. When S 2− pairs with Ca2+, Sr2+, or Ba2+, the resulting compound is soluble. When O H − pairs with Ca2+, Sr2+, or Ba2+, the resulting compound is slightly soluble. C O 32− and PO43− When these ions pair with L i +, N a +, K +, or N H 4 +, the resulting compounds are soluble.

Newton's laws of motion are deterministic. Explain this statement.

Deterministic behavior means that the present circumstances determines the future. This means that under identical conditions, identical results will occur.

Explain the wave behavior known as diffraction. Draw the diffraction pattern that occurs when light travels through two slits comparable in size and separation to the light's wavelength.

Diffraction occurs when a wave encounters an obstacle or a slit that is comparable in size to its wavelength. The wave bends around the slit. The diffraction of light through two slits separated by a distance comparable to the wavelength of the light results in an interference pattern. Each slit acts as a new wave source, and the two new waves interfere with each other. This results in a pattern of bright and dark lines.

How did the photoelectric effect lead Einstein to propose that light is quantized?

Einstein explained the photoelectric effect by proposing that light must consists of packets (particles). The amount of energy in a light packet depends on its frequency. The emission of electrons from a metal depends on whether or not a single photon has sufficient energy to dislodge a single electron.

Explain electron diffraction.

Electron diffraction occurs when an electron beam is aimed at two closely spaced slits, and a series of detectors is arranged to detect the electrons after they pass through the slits. An interference pattern similar to that observed for light is recorded behind the slits. Electron diffraction therefore provides evidence for the wave nature of electrons.

If energy flows out of a chemical system and into the surroundings, what is the sign of ΔEsystem?

Energy flowing out of the system is like a withdrawal from a checking account; therefore, it carries a negative sign.

What is heat? Explain the difference between heat and temperature.

Heat is the flow of thermal energy caused by a temperature difference. Thermal energy is a type of kinetic energy because it arises from the motions of atoms or molecules within a substance. The higher the temperature, the greater the motion of atoms and molecules. Heat is measured in units of energy (e.g. joules, calories, and kilowatt-hours), while temperature is measured in units of Kelvins, degrees Celsius, and degrees Fahrenheit.

What is Hess's law? Why is it useful?

Hess's law states that if a chemical equation can be expressed as the sum of a series of steps, then ΔHrxn for the overall equation is the sum of the heats of reactions for each step. This makes it possible to determine ΔH for a reaction without directly measuring it in the laboratory. If you can find related reactions (with known ΔH) that sum to the reaction of interest, you can find ΔH for the reaction of interest.

If the internal energy of the products of a reaction is higher than the internal energy of the reactants, what is the sign of ΔE for the reaction? In which direction does energy flow?

If the reactants have a lower internal energy than the products, ΔEsystem is positive and energy flows into the system from the surroundings.

Explain the principles behind an acid-base titration. What is an indicator?

In a titration, a substance in a solution of known concentration is reacted with another substance in a solution of unknown concentration. The acid-base titration is continued until the neutralization is complete. At the equivalence point, the point when the number of moles of OH⁻ equals the number of moles of H⁺, the titration is complete. An indicator is a dye whose color depends on the acidity or basicity of the solution.

What is calorimetry? Explain the difference between a coffee-cup calorimeter and a bomb calorimeter. What is each designed to measure?

In calorimetry, the thermal energy exchanged between the reaction (defined as the system) and the surroundings is measured by observing the change in temperature of the surroundings. A bomb calorimeter is used to measure the ΔErxn for combustion reactions. The calorimeter includes a tight-fitting, sealed container that forces the reaction to occur at constant volume. A coffee-cup calorimeter is used to measure ΔHrxn for many aqueous reactions. The calorimeter consists of two Styrofoam coffee cups, one inserted into the other, to provide insulation form the laboratory environment. Because the reaction happens under conditions of constant pressure (open to the atmosphere). Qrxn=qp=ΔHrxn

Describe the Bohr model for the atom. How did the Bohr model account for the emission spectra of atoms?

In the Bohr model, electrons travel around the nucleus in circular orbits (stationary states) that exist only at specific, fixed distances from the nucleus. The energy of each orbit is also fixed, or quantized. Bohr further proposed that no radiation was emitted by an electron orbiting the nucleus in a stationary state. It was only when an electron jumped, or made a transition, from one stationary state to another that radiation was emitted or absorbed. The electron is never observed between states. The emission spectrum of an atom consists of discrete lines because the stationary states exist only at specific, fixed energies.

An electron behaves in ways that are at least partially indeterminate. Explain this statement.

Indeterminacy means that the present circumstances do not necessarily determine future events in the quantum-mechanical realm. If an electron were to be thrown, it would land in a different place every time, even if it were thrown in exactly the same way.

Explain the wave behavior known as interference. Explain the difference between constructive and destructive interference.

Interference is the superposition of two or more waves overlapping in space, resulting in either an increase in amplitude, or a decrease in amplitude. Constructive interference is the interaction of waves from two sources that align with overlapping crests, resulting in a wave of greater amplitude. Destructive interference is the interaction of waves from two sources aligned so that the crest of one overlaps the trough of the other, resulting in cancelation.

What is light? How fast does it travel in a vacuum?

Light = electromagnetic radiation, which can be described as a wave composed of oscillating mutually perpendicular electric and magnetic fields propagating through space. -An electric field is a region where an electrically charged particle experiences a force. -A magnetic field is a region where a magnetized particle experiences a force Light travels at a speed of 3.00 x 10 ^8 m/s in a vacuum

What is an oxidation-reduction reaction? Give an example.

Oxidation-reduction reactions, or redox reactions, are reactions in which electrons are transferred from one reactant to the other. Many redox reactions involve the reaction of a substance with oxygen. An example is 4Fe(s) + 3O2(g) --> 2Fe2O3(s). (rusting)

What is pressure? What causes pressure?

Pressure is the force exerted per unit area by gas molecules as they strike the surfaces around them. Pressure is caused by collisions of gas molecules with surfaces or other gas molecules. Pressure=force/area

What reactant types give rise to gas-evolution reactions?

Some reactions form a gas directly from the ion exchange Other reactions form a gas by the subsequent decomposition of one of the ion exchange products into a gas and water The reactant types that give rise to gas-evolution are sulfides, carbonates, bicarbonates, sulfites, bisulfites, and ammonium compounds.

Explain Heisenberg's uncertainty principle. What paradox is at least partially solved by the uncertainty principle?

The Heisenberg uncertainty principle is the principle stating that due to the wave-particle duality, it is fundamentally impossible to precisely determine both the position and velocity of a particle at a given moment in time. Heisenberg solved the paradox of how a particle can be both a particle and a wave. By introducing complementarity, an electron is observed as either a particle or a wave, but never both at once.

What are the possible values of the angular momentum quantum number l? What does the angular momentum quantum number determine?

The angular momentum quantum number (L) is an integer that has possible values 1,2,3 and so on. The angular momentum quantum number determines the shape of the orbital. It can take values from 0 to (n-1) where n is the principal quantum number.

Define the frequency of electromagnetic radiation. How is frequency related to wavelength?

The frequency of a wave is the number of cycles that pass through a stationary point in one second. Frequency is inversely proportional to the wavelength.

What is heat capacity? Explain the difference between heat capacity and specific heat capacity.

The heat capacity of a system is usually defined as the quantity of heat required to change its temperature by 1oC. Heat capacity (C) is a measure of the system's ability to hold thermal energy without undergoing a large change in temperature. The difference between heat capacity (C) and specific heat capacity (Cs) is that the specific heat capacity is the amount of heat required to raise the temperature of 1 gram of the substance by 1oC.

What is internal energy? Is internal energy a state function?

The internal energy (E) of a system is the sum of the kinetic and potential energies of all of the particles that compose the system. Internal energy is a state function.

How is the change in internal energy of a system related to heat and work?

The internal energy (E) of a system is the sum of the kinetic and potential energies of all of the particles that compose the system. The change in the internal energy of the system (ΔE) must be the sum of the heat transferred (q) and the work done (w): ΔE=q+w.

From a molecular viewpoint, where does the energy absorbed in an endothermic chemical reaction go? Why does the reaction mixture undergo a decrease in temperature even though energy is absorbed?

The internal energy of a chemical system is the sum of its kinetic energy and its potential energy. It is this potential energy that absorbs the energy in an endothermic chemical reaction. In an endothermic reaction, as some bonds break and others form, the protons and electrons go from an arrangement of lower potential energy to one of higher potential energy, absorbing thermal energy in the process. This absorption of thermal energy reduces the kinetic energy of the system. This is detected as a drop in temperature.

From a molecular viewpoint, where does the energy emitted in an exothermic chemical reaction come from? Why does the reaction mixture undergo an increase in temperature even though energy is emitted?

The internal energy of a chemical system is the sum of its kinetic energy and its potential energy. It is this potential energy that is the energy source in an exothermic chemical reaction. Under normal circumstances, chemical potential energy (or simply chemical energy) arises primarily from the electrostatic forces between the protons and electrons that compose the atoms and molecules within the system. In an exothermic reaction, some bonds break and new ones form and the protons and electrons go from an arrangement of higher potential energy to one of lower potential energy. As they rearrange, their potential energy is converted into kinetic energy, the heat emitted in the reaction. This increase in kinetic energy is detected as an increase in temperature.

What are the possible values of the magnetic quantum number ml? What does the magnetic quantum number determine?

The magnetic quantum number (ml) is an integer ranging from -l to +l. For example if l=1, ml = -1,0,+1. The magnetic quantum number specifies the orientation of the orbital.

What is the Schrödinger equation? What is a wave function? How is a wave function related to an orbital?

The mathematical derivation of energies and orbitals for electrons in atoms comes from solving the Schrödinger equation. The general form of the Schrödinger equation is HΨ = EΨ. The symbol H stands for the Hamiltonian operator, a set of mathematical operations that represent the total energy (kinetic and potential) of the electron within the atom. The symbol E is the actual energy of the electron. A plot of the wave function squared (Ψ^2) represents an orbital, a position probability distribution map of the electron.

Describe the photoelectric effect. How did the experimental observations of this phenomenon differ from the predictions of classical electromagnetic theory?

The photoelectric effect is the observation that many metals emit electrons when light falls upon them. Classical electromagnetic theory predicted that changing either the wavelength or the amplitude of the light would affect the emission of electrons. In addition, a dim light would be expected to result in a lag time between the initial shining of the light and the subsequent emission of an electron. Experimental results showed, however, that a high-frequency, low-intensity light produced electrons without the predicted lag time. Furthermore, the light used to dislodge electrons exhibited a threshold frequency, in which low-frequency light would not eject electrons from a metal regardless of its intensity or its duration. But high-frequency light would eject electrons, even if the intensity was low.

What are the possible values of the principal quantum number n? What does the principal quantum number determine?

The principle quantum number (n) is an integer that has possible values 1,2,3, and so on. The principal quantum number determines the overall size and energy of an orbital.

Explain the difference between a plot showing the probability density for an orbital and one showing the radial distribution function.

The probability density is the probability per unit volume of finding the electron at a point in space. The radial distribution function represents the total probability of finding the electron within a thin spherical shell at a distance r from the nucleus. In contrast to probability density, which has a maximum at the nucleus for an s orbital, the radial distribution function has a value of zero at the nucleus. It increases to a maximum and then decreases again with increasing r.

Why is the quantum-mechanical model of the atom important for understanding chemistry?

The quantum mechanical model is important to understanding chemistry because it explains how electrons exist in atoms and how those electrons determine the chemical and physical properties of the elements. -Why some elements are metals and others are nonmetals. -Why some elements gain one electron when forming an anion, whereas others gain two. -Why some elements are very reactive, while others are practically inert. -Why, in other periodic patterns, we see the properties of the elements.

Determine the color of a colored object? Explain why grass appears green.

The reflection of certain wavelengths of visible light and the absorption of all other wavelengths of visible light determines the color of a colored object. Grass appears green because of the reflection of green light and the absorption of all other colors.

What are the solubility rules? How are they useful?

The solubility rules are a set of empirical rules that have been inferred from observations on many ionic compounds. The solubility rules allow us to predict whether a compound is insoluble or soluble.

What is the standard enthalpy of formation for a compound? For a pure element in its standard state?

The standard enthalpy of formation (ΔHof) for a pure compound is the change in enthalpy when 1 mole of the compound forms from its constituent elements in their standard states. For a pure element in its standard state, ΔHof =0.

What is a standard state? What is the standard enthalpy change for a reaction?

The standard state is defined as follows: for a gas, the pure gas at a pressure of exactly 1 atm; for a liquid or solid, the pure substance in its most stable form at a pressure of 1 atm and the temperature of interest (often taken to the be 25oC; and for a substance in solution, a concentration of exactly 1 M. The standard enthalpy change (ΔHo) is the change in enthalpy for a process when all reactants and products are in their standard states. The superscript degree sign indicates standard states.

List the four different sub levels. Given that only a maximum of two electrons can occupy an orbital, determine the maximum number of electrons that can exist in each sub level.

The sub levels are s(l=0), which can hold a maximum of two electrons; p(l=1), which can hold a maximum of 6 electrons; d (l=2), which can hold a maximum of 10 electrons, and f(l=3) which can hold a maximum of 14 electrons.

Why does the uncertainty principle make it impossible to predict a trajectory for the electron?

The uncertainty principle makes it impossible to predict a trajectory for the electron because we cannot simultaneously know the position and velocity of the electron. The future path of an electron is indeterminate, and can only be described statistically.

What is pressure-volume work? How is it calculated?

The work caused by an expansion of volume is simply the negative of the pressure that the volume expands against multiplied by the change in volume that occurs during the expansion: w=-PΔV.

What happens to a substance when it becomes oxidized? Reduced?

When a substance is oxidized, it loses electrons and there is an increase in oxidation state. When a substance is reduced, it gains electrons and there is a reduction in oxidation state.

How do you calculate ΔHorxn from tabulated standard enthalpies of formation?

To calculate ΔHorxn subtract the heats of formations of the reactants multiplied by their stoichiometric coefficients from the heats of formation of the products multiplied by their stoichiometric coefficients. In the form of an equation:i. ΔHorxn =Σnp ΔHof (products)-Σnp ΔHof(reactants)

How can oxidation states be used to identify redox reactions?

To identify redox reactions using oxidation states, begin by assigning oxidation states to each atom in the reaction. A change in oxidation state for the atoms indicates a redox reaction. •Any reaction in which there is a change in the oxidation states of atoms in going from reactants to products. In a redox reaction: •The oxidizing agent oxidizes another substance (and is itself reduced). •The reducing agent reduces another substance (and is itself oxidized).

For each solution to the Schrodinger equation, what can be precisely specified: the electron's energy or its position? Explain.

Using the Schrödinger equation, we describe the probability distribution maps for electron states. In these the electron has a well-defined energy, but not a well-defined position. In other words, for each state, we can specify the energy of the electron precisely but not its location at a given instant. The electron's position is described in terms of an orbital.

What determines the color of light? Describe the difference between red light and blue light.

Wavelength determines the color of visible light. Red and blue light consists of different wavelengths. Red light has a wavelength of about 700 nm and blue light has a wavelength of about 450 nm.

Why do deep-sea divers breathe a mixture of helium and oxygen?

When a diver breathes compressed air, the abnormally high partial pressure of oxygen in the lungs leads to an elevated concentration of oxygen in body tissues. •Helium is inert so if it is absorbed, will not cause problems •lighter

If two objects, A and B, of different temperature come into direct contact, what is the relationship between the heat lost by one object and the heat gained by the other? What is the relationship between the temperature changes of the two objects? (Assume that the two objects do not lose any heat to anything else.)

When two objects of different temperatures come in direct contact, heat flows from the higher temperature object to the lower temperature object. The amount of heat lost by the warmer object is equal to the amount of heat gained by the cooler object. The warmer object's temperature will drop and cooler object's temperature will rise until they reach the same temperature. The magnitude of these temperature changes depends on the mass and heat capacities of the two objects.

How can you predict whether a precipitation reaction will occur upon mixing two aqueous solutions?

You can predict by understanding that only insoluble compounds form precipitates. In a precipitation reaction, 2 solutions containing soluble compounds combine and an insoluble compound precipitates. 1.Determine what ions constitute each aqueous reactant. 2.Determine formulas of possible products. -Exchange ions. (+) ion from one reactant with (−) ion from other -Balance charges of combined ions to get the formula of each product. 3.Determine solubility of each product in water. -Use the solubility rules. -If the product is insoluble or slightly soluble, it will precipitate. 4.If neither product will precipitate, write no reaction after the arrow. 5.If any of the possible products are insoluble, write their formulas as the products of the reaction using (s) after the formula to indicate solid. Write any soluble products with (aq) after the formula to indicate aqueous. 6.Balance the equation. -Remember to change only coefficients, not subscripts.

Explain how the value of ΔH for a reaction changes upon each operation: a. Multiplying the reaction by a factor: b. Reversing the reaction: c. Why do these relationships hold?:

a. Multiplying the reaction by a factor:If a reaction is multipled by a factor, the ΔH is multipled by the same factor. b. Reversing the reaction:If a reaction is reversed, the sign of ΔH is reversed. c. Why do these relationships hold?:The relationships hold because H is a state function. Twice as much energy is contained in twice the quantity of reactants or products. If the reaction is reversed, the final and initial states have been switched and the direction of heat flow is reversed.

What is the change in enthalpy (ΔH) for a chemical reaction? How is ΔH different from ΔE?

ΔH is the heat exchanged with the surroundings under conditions of constant pressure. ΔH is equal to qp, the heat at constant pressure. Conceptually (and often numerically), ΔH and ΔE are similar: they both represent changes in a state function for the system. However, ΔE is a measure of all of the energy (heat and work) exchanged with the surroundings. ΔH=ΔE+PΔV

Is the change in enthalpy for a reaction an extensive property? Explain the relationship between ΔH for a reaction and the amounts of reactants and products that undergo reaction.

ΔHrxn is an extensive property; therefore, it depends on the quantity of reactants undergoing reaction. ΔHrxn is usually reported for a reaction involving stoichiometric amounts of reactants and is dependent on the specific chemical reaction. For example, for a reaction A+2B→C, ΔHrxn is usually reported as the amount of heat emitted or absorbed when 1 mole of A reacts with 2 moles of B to form 1 mole of C.

How is kinetic energy of a gas related to temperature? How is the root mean square velocity of a gas related to its molar mass?

•Average KE proportional to T in K •root mean square velocity is inversely proportional to square root of molar mass of particles in kg/mol

Explain how the ideal gas law contains within it the simple gas laws. Show an example.

•Boyles law: V inversely related to P •Charles Law: V directly related to T •Avogadro's law: V directly related to n •we get V=RnT/P rearranged = PV=nRT

Explain the difference between diffusion and effusion. How is the effusion rate of a gas related to its molar mass?

•Diffusion: spread out in response to a concentration gradient, high concentration to low concentration •Effusion: gas escapes from container into a vacuum through a small hole •rate inversely proportional to square root of molar mass of gas

What is Law of Conservation of Energy? How does it relate to energy exchanges between a thermodynamic system and its surroundings?

•Energy not created or destroyed •energy transferred •if system loses, surrounding gain and vice versa

What is energy? What is work? List examples.

•Energy: capacity to do work ex. KE, heat, electrical, chemical, light •Work: result of force and distance ex. moving an object, running Energy=work=force x distance

What is Kinetic Energy? What is Potential Energy? List examples.

•KE is energy of motion ex. moving ball, raging river •PE is energy of position ex. ball held above ground, compressed spring

When a gas is collected over water, is the gas pure? Why? How can the partial pressure of the collected gas be determined?

•No, it will contain some water molecules •vapor pressure of water can be known, subtract from total pressure to get partial pressure

What is thermochemistry and why is it important?

•Study of relationship between chemistry and energy •energy and uses are critical to society

What is the ideal gas law? Why is it useful?

•The relationships that we have discussed so far can be combined into a single law that encompasses all of them. •By combining the gas laws, we can write a general equation. •R is called the gas constant. •The value of R depends on the units of P and V. -We will use P V = n R T, with P in atm and V in liters. •The other gas laws are found in the ideal gas law if two variables are kept constant. •The ideal gas law allows us to find one of the variables if we know the other three. V=RnT/P

What is the first law of thermodynamics? What are its implications?

•Total energy of the universe is constant •with energy you cannot get something for nothing •Therefore, you can never design a system that will continue to produce energy without some source of energy.

How does the density of a gas depend on temperature? Pressure? How does it depend on the molar mass of the gas?

•d=PM/RT •density will decrease as temperature increases •density will increase as pressure increases •density will increase as molar mass increases

Define molar volume and give its value for a gas at STP.

•molar volume: volume occupied by a mole at STP (T=273 K= 0=C, P=1 atm). 22.4

Describe how the molecules in a perfume bottle travel fro the bottle to your nose. What is mean free path?

•molecule travels short distance, collides with another and changes direction •average distance a molecule travels between collisions

What is partial pressure? What is the relationship between the partial pressures of each gas in a sample and the total pressure of gas in the sample?

•pressure due to any individual component in a gas mixture •can be found from ideal gas law assuming each gas component acts independently •sum of total partial pressures give total pressure

If a reaction occurs in the gas phase at STP, the mass of a product can be determined from the volume of reactants. Explain.

•we know coefficients in chemical equations used as conversion factors between number of moles •we know each mole of gas occupies 22.4 L, we need to find the moles of each reactant, find which is limiting and use mole ratio to find moles of product