Exam 3 PLQs

Gay-Lussac's Law

(P1 / T1) = (P2 / T2) -Volume and number of moles n are constant so the gas law that we need will have only pressure and temperature as variables. -An increase in temperature means an increase in the average kinetic energy and urms. Since there is no change in volume, there are more collisions with the walls per unit time, and the collisions are more forceful, increasing the gas pressure. This is one of the reasons that closed gas containers should not be heated, as they may explode.

Kelvin

(T(K) = T(°C) + 273.15) -the SI base unit of temperature.

What is the difference between u and ums? Be sure to define both.

- the square of their average speed (u). - mean square average speed

What additional types of electrostatic interactions are present in non-ionic particles?

-An induced dipole is an instantaneous temporary dipole moment that results when the electron cloud of a particle is distorted. -Dispersion forces, dipole-dipole, hydrogen bonds.

What does it mean for a process to be isothermal? Given an example of an isothermal process.

-At a certain temperature some of the particles have sufficient kinetic energy to break loose from these interactions and start moving past each other. The solid starts to melt. Further addition of heat does not lead to an increase in temperature; instead, the supplied energy is used to break intermolecular attractions throughout the solid. -This process of fusion is isothermal, meaning the temperature remains constant until the entire solid has melted; the temperature at which this happens is called the melting point.

What is Boyle's law and what is the relationship between pressure and volume?

-Boyle's law quantifies the relation between volume and pressure of a sample of gas at constant temperature. -The results show that there is an inverse relationship between pressure and volume: as the volume of a fixed amount of gas at constant temperature decreases its pressure increases.

Describe ion-dipole interactions and give an example.

-Coulombic (electrostatic) attractions between ions and polar molecules. Ion-dipole forces = the force that exists between an ion and a neutral polar molecule that possesses a permanent dipole moment. Ion-dipole = ions in polar liquids. Na+/H2O

What is the difference between BC and DE? (Why is DE longer than BC?) What does that tell you about water?

-DE takes more energy to break the intermolecular interactions. -Water has a high boiling point.

What are London dispersion forces? What molecular properties determine the strength of these forces?

-Dispersion forces in helium. The momentary asymmetry of electrons around neutral helium (green) creates a dipole that polarizes helium atoms in close proximity (rainbow color). The induced dipoles attract each other and polarize more helium atoms. -The attraction forces due to such "self-polarization" are called London dispersion forces (LDF), or just dispersion forces. -Their strength depends on the polarizability of atoms or molecules, which can be thought of as the squashiness of the electron cloud; the more polarizable the electron density, the stronger the interactions. -In general, the polarizability increases with the number of electrons; heavier and bigger atoms or molecules have stronger dispersion forces than do lighter particles.

Under what conditions are the deviations from ideal gas behavior noticeable?

-For most gases the deviations are quite small at low pressures, but become quite apparent at higher pressures. -The magnitude of the deviations also depends on temperature, with smaller deviations observed at higher temperatures.

What properties of water can be attributed to its hydrogen bonding capabilities?

-Hydrogen bonds are generally stronger than dipole-dipole forces or London dispersion forces, and if present in the substance, they usually provide the largest contribution to intermolecular interaction, resulting in higher melting and boiling points relative to similar compounds lacking hydrogen bonds. Like other intermolecular forces, they are additive; molecules capable of forming multiple hydrogen bonds have dramatically increased intermolecular interactions. -Solid water (ice) is less dense than the liquid phase, thanks to the highly organized network of hydrogen bonds (four per water molecule) that support a structure with large voids (Figure F11-5-3), which collapse on melting. As a consequence, water expands when it freezes, and ice floats on top of water. Without this property aquatic life would not be able to survive in frozen lakes in the winter.

Draw pictures to show the difference between effusion and diffusion.

-In effusion, gases escape through a tiny hole. -in diffusion, they spread through space or through another substance (a gas, for example).

What factors are responsible for the weakening of dipole-dipole interactions in the liquid as compared to the solid?

-In the solid phase the molecules are neatly arranged, with the positively-charged ends of their dipoles (the -CH3 end) close to the negatively-charged ends of the dipoles on nitrogen atoms. This arrangement minimizes positive-positive and negative-negative repulsive interactions. -In the liquid phase, the molecules move constantly, rearranging their positions and orientations. There are, on average, more attractive than repulsive interactions, but the molecules are much more disordered and separated (the density of the solid is higher than the density of the liquid). -Both of these factors are responsible for weaker intermolecular interactions in the liquid phase.

What phases are exothermic? Which are endothermic? Is there a trend here? What do you notice?

-Melting, vaporization, and sublimation are endothermic. -Freezing, condensation, and deposition are exothermic. -Going from solid to liquid to gas, enthalpy increases and there is a endothermic process. -Going from gas to liquid to solid, enthalpy decreases and there is an exothermic process.

What is R? How do you know which value of R to use?

-R is the gas constant, or proportionality constant. -The value of R depends on the units used for the variables of state. -The equivalent of the gas constant "per-molecule" is the Boltzmann constant (kB = R/NA). *Look at table for common values. T12-4-1

What are the SI units of pressure?

-The SI unit of pressure is the pascal (1 Pa = 1 N/m2 where N is newtons and m is meters). -Pressure can also be described using units of the bar (1 bar = 105 Pa).

Compare intramolecular forces to intermolecular forces in terms of their strengths and range in which they act.

-The bonds between atoms are the intramolecular forces responsible for maintaining the integrity of discrete molecules or extended networks. They are strong, directional (i.e. point from an atom to its bonding partners) and act at short range (the nuclei are short distances from each other). -Intermolecular forces occur between neighboring molecules; they are generally weaker than chemical bonds, are less directional, and operate at longer range (the nuclei of the interacting particles do not get very close).

What is STP?

-The conditions of 1 atm and 0 °C are called the standard temperature and pressure (STP). -the volume occupied by one mole of gas under STP conditions is called the molar volume of an ideal gas (VSTP).

What is the definition of polarizability? Which attractive force is related to the polarizability of a molecule?

-The ease with which the electron density cloud is distorted is called the polarizability (α). : the ease with which the electron cloud of an atom or a molecule is distorted by an outside influence thereby inducing a dipole moment. -Attractive forces produced by these temporary dipole moments are known as dispersion forces (also called London dispersion forces, or LDFs).

What are the other 4 phase transitions? Which are exothermic and which are endothermic?

-The liquid to gas (vapor) transition is called vaporization. It is an endothermic process. -Sublimation (solid to gas) and vaporization (liquid to gas) are endothermic. -Condensation (gas to liquid) and deposition (gas to solid) are exothermic.

Rank the molecules according to increasing melting point.

-The molecule with the strongest IMFs will have the highest melting point and the molecule with the weakest IMFs will have the lowest melting point. -London dispersion forces increase in strength as the polarizability of the molecule increases. Polarizability increases as the number of electrons (as the size) increases.

Why do we call this type of interaction a hydrogen "bond"? How does it differ from other intermolecular forces?

-The name of the hydrogen bond denotes both the increased strength of the interactions and its directionality, similar to covalent bonds. -Hydrogen bonds are stronger than other dipole-dipole and dispersion forces, (but are weaker than covalent bonds).

What is the van der Waals radius of a molecule? What determines this radius?

-The nonbonding distances are known as the van der Waals radii, and represent the distances at which the dispersion and dipole-dipole interactions stop being attractive -This is also the minimum possible distance between molecules in the condensed phase.

What is the relationship between rate of effusion or diffusion and molar mass?

-The rate of effusion of a gaseous substance is inversely proportional to the square root of its molar mass. -Thus the rate at which a molecule, or a mole of molecules, diffuses or effuses is directly related to the speed at which it moves.

What is the relationship between molecular speed and temperature as the molar mass stays constant?

-The speed of the molecules in a gas is proportional to the temperature and is inversely proportional to molar mass of the gas. -In other words, as the temperature of a sample of gas is increased, the molecules speed up and the root mean square molecular speed increases as a result.

What is the melting point?

-The temperature at which solid and liquid phases of a substance are in equilibrium. -The melting point is a characteristic property of the pure substance, and it is a measure of the strength of the intermolecular interactions in the solid.

How are these parameters related to the properties of a real gas?

-These deviations are due to intermolecular forces, which cause a decrease the pressure of the gas, and the actual volume of molecules themselves, which results in a larger value for the total volume of the gas compared to what the ideal gas law predicts.

What are the causes of this deviation from the ideal gas prediction?

-These deviations can be explained by two main factors: real gas molecules have finite sizes, and real gas molecules do interact through intermolecular forces. -Under high pressures, the value of PV/RT is greater than the expected value of 1 (for example, see H2 or N2 in F12-5-1). At constant temperature and with an unchanging number of moles, this means that the apparent volume of a gas sample is greater than would be predicted by the ideal gas law. -The intermolecular attractions make the apparent pressure smaller than that predicted by the ideal gas law.

Why are heats of vaporization larger than heats of fusion?

-This is because all intermolecular interactions in liquid are broken upon vaporization, but many of the interactions in solids remain after melting since molecules are still in close contact.

Explain the difference between the two plots in F12-3-3. How can both of them be an representation of Boyle's Law?

-V as a function of P, or with P as a function of 1/V. Because P and V are inversely proportional, when comparing the same sample of gas at two sets of volume and pressure, or two gases at constant temperature and number of moles of particles. P1V1=P2V2

List three examples of everyday situations where phase transitions facilitate the transfer of heat.

-We cool our drinks by adding ice; the heat needed to melt the ice is taken from the drink, lowering its temperature. -In hot weather we sweat, and the evaporating water withdraws heat (needed for evaporation) from our skin, providing a mechanism to regulate our body temperature. -Refrigerators cool by withdrawing heat from the food compartment and using it to evaporate liquids with low boiling points (usually under reduced pressure).

What is the relationship between the number of collisions and pressure?

-Weight of the air column actually makes the air denser closer to the Earth's surface, which in turn leads to more collisions per second. -Higher gas density means more collisions per unit time per area and thus higher pressure.

What does it mean for a gas and liquid to be in equilibrium?

-When the rate of escape is equal to the rate of reentry into the liquid phase, equilibrium is established between the liquid and vapor phases. -a state in which forward and reverse processes are occurring at the same rates.

What is a phase diagram? (What are the axis labels? What is depicted in the diagram?) Describe a general phase diagram.

-a graphic representation of the equilibria among the solid, liquid, and gaseous phases of a substance as a function of temperature and pressure. -illustrate phases and phase transitions as a function of temperature and pressure -Y axis is pressure and x axis is temperature.

What is Charles' law and the relationship between volume and temperature? How can this relationship be predicted using KMT?

-a volume of a sample of gas is proportional to the absolute temperature if kept at constant pressure. -the volume of a fixed amount of gas, maintained at constant pressure, is directly proportional to the absolute temperature. -as the temperature drops, so does the kinetic energy of the particles (and their average speed). There are fewer collisions per unit time and the collisions are less energetic. Since the number of moles of gas and the pressure must remain constant, the only solution is to shrink the volume occupied by the gas.

What is standard atmospheric pressure?

-defined as 1 atm or 760 torr (i.e. mmHg) or, in SI units, 101.325 kPa; a typical pressure at the sea level.

What is the enthalpy of vaporization?

-enthalpy of fusion the enthalpy change when a substance vaporizes: the quantity of energy that must be transferred from the surroundings to the system when it transitions from liquid phase to the gas phase at constant temperature and pressure -(ΔHvap)

What are the four variables that define the state of a gas sample?

-pressure (P) -volume (V) -temperature (T) -the amount of gas particles, usually expressed in moles (n)

How do we determine the heat of sublimation?

-the enthalpy of sublimation is equal to the sum of the enthalpies of fusion and vaporization. -(ΔHsub = ΔHfus + ΔHvap).

What are van der Waals forces?

-the noncovalent force of attraction between any two polar molecules or polar regions in the same large molecule, -dipole-dipole attractions (collectively called van der Waals forces or vdWF).

What is the vapor pressure?

-the partial pressure exerted by the vapor in equilibrium with its liquid or solid phase in a sealed container at a given temperature.

What is the definition of vapor pressure?

-the partial pressure exerted by the vapor in equilibrium with its liquid or solid phase in a sealed container at a given temperature. -represents a dynamic equilibrium between molecules in the liquid phase and molecules in the gas phase of a substance

What is Dalton's Law of partial pressure? In addition to defining this, give an equation that represents the definition.

-the pressure of a mixture of gases equals the sum of the partial pressures of the components. Pt = P1 + P2 + P3 + ... = nt (RT / V)

What is the definition of heat capacity?

-the quantity of energy that must be transferred to an object to raise its temperature by 1 °C (or 1 K). -In fact, for pure substances (like ice) the heat capacity is either called the molar heat capacity (Cm) if given per mole, or the specific heat capacity (Cs), (sometimes just called specific heat) if given for 1 gram of the substance.

What is the boiling point of a liquid?

-the temperature at which the equilibrium vapor pressure of a liquid equals the external pressure on the liquid (atmospheric pressure, unless the vessel containing the liquid is closed). -value is indicative of the strength of the intermolecular interactions in the liquid. -When a liquid changes into a gas there is an immense change in volume (more than 1000-fold for water, for example). -The temperature of the boiling liquid remains constant until all liquid is transformed into vapor. The energy provided during this phase transition is used to break all of the remaining intermolecular interactions.

What do we mean by absolute zero? How does Charles's Law lead to this? (What assumption do we have to make to determine absolute zero?)

-theoretically the lowest obtainable temperature: −273.15 °C or 0 K. The thermal energy of motion vanishes, in agreement with the definition of temperature derived from kinetic molecular theory -If we examine the Charles's law plots for a few different constant pressures, we find an interesting phenomenon. As the temperature is lowered, all the lines converge and can be extrapolated to a volume of zero. We cannot actually carry the cooling that far since gases liquefy, but the result still has a profound significance.

What is Avogadro's Law? How can this relationship be predicted using KMT?

-under constant temperature and pressure, the volume of a gas is directly proportional to the number of moles of gas. -this law explains how equal volumes of all gases contain the same number of molecules when T and P are held constant, and why the ratios of volumes of reacting gases and their products can be expressed with a simple whole number. -the mean-square speed is constant at constant T, and if P is also constant, V is directly proportional to N (N is the number of particles, which is proportional to the number of moles, n). If the number of moles of particles in the container increases, the volume must also increase in order to maintain a constant pressure.

Which molecules in Groups 5A, 6A and 7A exhibit exceptionally high boiling points? Why?

-water (H2O), ammonia (NH3), and hydrogen fluoride (HF) all show strong deviations; they all have substantially higher boiling points than expected. -The extraordinary deviations from the boiling-point trends observed for NH3, H2O and HF are due to hydrogen bonding, which is a special case of directional dipole-dipole interactions

List the basic four assumptions of the kinetic molecular theory.

1. Gases consist of a large number of very small particles (molecules or atoms) in constant, random motion. 2. The molecules are separated by distances that are far greater than their sizes. In other words, the total volume of all molecules is negligible compared to the volume of the gas sample. 3. The molecules exert no forces on each other (i.e. there are no intermolecular interactions), and between collisions they move in straight lines with constant velocities. 4. All collisions with other molecules and with the walls of the container are elastic, i.e., no kinetic energy is lost during the collisions.

Describe the correlation between number of carbons in an alkane and the boiling point.

As the number of carbon atoms increases or the length of carbon-carbon chain increases, the boiling point also increases. This is because the force of attraction between the molecules increases as the molecule gets longer and has more electrons.

How does kinetic molecular theory (KMT) be used to predict this experimental behavior?

At constant temperature the root mean square speed (urms) does not change. Therefore, when the volume is decreased the molecules travel a shorter distance between collisions, and there are more collisions per unit time: the pressure increases with the number of collisions.

Why are boiling chips added to liquids when they are heated in the laboratory?

Boiling chips provide nucleation sites so the liquid boils smoothly without becoming superheated or bumping.

Equations (Boyle's, Avogadro's, Charles')

Boyle : P1 V1 = P2 V2 Avogadro : (n1 / V1) = (n2 / V2) Charles : (V1 / T1) = (V2 / T2)

Compare the Van der Waals constants for Ne and CCl4, explaining how the constants are connected to properties of these gases.

CCl4 has a higher a and b, so a greater magnitude of attractive forces between the molecules and volume occupied by the gas molecules in the van der Waals equation.

What remains unchanged when phase transitions occur?

Changing the amount of heat energy usually causes a temperature change. However, DURING the phase change, the temperature stays the same even though the heat energy changes. This energy is directed into changing the phase and not into raising the temperature. -There is no change in the chemical formula of a molecule or the types and numbers of chemical bonds as it undergoes a phase transition. Many substances can exist as any of the three phases within relatively narrow ranges of pressure and temperature.

What do we mean by thermal energy?

Even though the particles in bulk materials are in close contact, the particles are in constant motion. They vibrate or move and collide with each other and with the walls that contain them. In these collisions they transfer and redistribute their kinetic energy. -This incessant movement constitutes the thermal energy of the sample.

What are the assumptions made for ideal gas behavior?

For a gas to be "ideal" there are four governing assumptions: -The gas particles have negligible volume. -The gas particles are equally sized and do not have intermolecular forces (attraction or repulsion) with other gas particles. -The gas particles move randomly in agreement with Newton's Laws of Motion.

How does the distance between dipoles effect the dipole-dipole interaction?

For ion-ion interactions, if the distance between ions increases by the factor of two, the interaction energy also decreases by a factor of two. For dipole-dipole interactions, the same change in distance between dipoles leads to an 8-fold decrease in the interaction energy.

In general what kind of molecules exhibit hydrogen bonding? Give an example.

Hydrogen bonds are formed when hydrogen atoms bonded to F, O, and N interact with electron pairs on electronegative elements, especially F, O, and N. -Only electron pairs on the most electronegative neutral atoms (F, O, N) participate in hydrogen bonding, accepting the positively-polarized hydrogen. H2O, HF, NH3.

What is the major difference between line AB and that of BC?

In AB temperature changes, but in BC it stays the same.

What are intra molecular forces? What are intermolecular forces?

Intra = existing or taking place within a molecule ("intra" = "within"). Inter = noncovalent short-range attractive forces between separate molecules, responsible for holding particles together in the condensed phases.

List examples of intermolecular interactions, (i.e., what molecules or ions interact in each type of intermolecular interaction?).

Ion-dipole = ions in polar liquids. Dipole-dipole = polar liquids or solids. Ion-induced dipole = ions in nonpolar liquids. Dipole-induced dipole = nonpolar molecules in polar solvents. Dispersion = nonpolar liquids or solids. Hydrogen bonding = H bonded to N, O, F.

Why are ionic bonds strong?

Ionic bonds are strong because ions with full charges (or even multiple charges) attract each other with energy that is proportional to the charge (Q) and inversely proportional to the distance between them (1/d).

What are the important IMFs in five molecules given? Do the IMFs present help explain the trend in boiling point?

LDF forces and dipole-dipole. -The molecule with the greatest boiling point will have the strongest IMF. CCl4 has the highest boiling point, so even though it is nonpolar, it has the strongest IMFs of the given set of molecules.

Explain how partial pressure can determined using mole fraction.

P1 = (n1 / nt) Pt = X1Pt

Give an example of two or more types of compounds that have structures and properties that are linked to their H-bonding capabilities.

Proteins, (the key structural elements of living organisms), enzymes (responsible for anabolism and metabolism), receptors (crucial to cell signaling) and DNA (the repository of the genetic code of living organism) all maintain their structures and function because of hydrogen bonding. Life as we know it depends upon hydrogen bonding.

When liquid phase molecules evaporate at constant T, what can we say about the kinetic energy of the liquid and vapor?

Since our experiment is run at constant temperature by providing heat from the surroundings to maintain the temperature, the average kinetic energies of both phases remain the same.

Using terms of intermolecular interactions and thermal energy, describe the transition from a solid to a liquid.

Solids melt when the molecules acquire enough thermal energy to overcome the intermolecular forces that lock them into place in the solid. -If we increase the thermal energy by increasing the temperature, the molecules, on average, will vibrate faster and with larger amplitudes. Eventually, the molecules will gain sufficient energy to break some of the intermolecular attractions to their neighbors, and will break out of the organized pattern of the solid; they will start moving past each other and the solid will turn into a liquid. The temperature at which this happens is called the melting point.

What is the enthalpy of fusion?

The amount of energy required to melt a substance is called the enthalpy of fusion (ΔHfus), or sometimes the heat of fusion. -the enthalpy change when a substance melts; the quantity of energy that must be transferred from the surroundings to the system when it transitions from the solid phase to the liquid phase at constant temperature and pressure

Describe the correlation between intermolecular forces and boiling point.

The boiling point is the measure of the strength of intermolecular interactions in a liquid: the stronger the interactions, the higher the boiling point. -The stronger the IMFs, the lower the vapor pressure of the substance and the higher the boiling point. -Pressure also affects the distance between molecules, and thus affects the strength of their interactions (the closer they are the stronger the IMF).

When the results of Boyle's Law, Charles's Law and Avogadro's Law are combined, what equation do we end up with?

The ideal gas law = An ideal gas is defined as any gas that obeys the kinetic molecular theory postulates : Specifically, the volume of molecules must be significantly smaller than the volume occupied by the gas, and the molecules of gas cannot have any intermolecular interactions. P V = n R T

Explain how the ideal gas law can also be related to the density of a gas.

The ideal gas law can also be related to the density of a gas (d = mass per unit volume) by dividing both sides of E12-4-1 by V and RT and multiplying by ℳ (the molar mass): d = (nM / V) = (PM / RT)

Explain how the plots in F12-5-1 illustrate the non-ideal behavior of gases.

The ideal gas law predicts that PV/RT should equal 1.0 (for 1 mole of gas) for all values of pressure. Real gases deviate from this prediction as shown in Figure (F12-5-1). -Deviations from the ideal gas law for several gases at 300 K (left), and for nitrogen gas at different temperatures (right).

As molar mass increases, boiling point increases. Explain why this is true.

The longer the alkane gets (higher molecular weight), the more intermolecular forces are present (London Dispersion), and this increases the melting and boiling points.

What molecular property is proportional to the size of the induced dipole of a molecule?

The magnitude of this induced dipole will be proportional to the polarizability (α).

Why do the 3 isomers of pentane have different boiling points?

The more branched the chain, the lower the boiling point tends to be. Van der Waals dispersion forces are smaller for shorter molecules and only operate over very short distances between one molecule and its neighbors.

What is the definition of fusion? Is the process exothermic or endothermic?

The phase transition from solid to liquid, called fusion (or melting) is endothermic.

What factors influence the strength of the dipole-dipole interaction?

The strength of dipole-dipole interactions depends on the orientation of interacting molecules, and diminishes strongly with increasing intermolecular distances.

What process is the reverse of fusion? What is the enthalpy for this process?

The transition in the reverse direction, from liquid to solid, is called freezing. It is an exothermic process. -The enthalpy of the process is still called the heat of fusion, except it has a negative algebraic sign in accordance with conventions for exothermic heat transfer.

What parameters are introduced into the ideal gas law by Johannes Van der Waals?

The van der Waals equation takes into account molecular volume and intermolecular forces in order to quantify deviations from ideal gas behavior.

What is a distribution function? Compare the distribution of exam scores for a class of students to the distribution of speeds of molecules.

This function describing allocations of molecular speeds is called a Maxwell-Boltzmann distribution.

What is the name of the energy change that occurs at constant pressure?

Under conditions of constant pressure, the energy change equals a change in enthalpy (ΔH).

Which intermolecular forces dominate in larger molecules? (Compare the bp for HCl, HBr and HI. What type of intermolecular force increases as the bp increases?)

When molecules differ substantially in size (i.e. molecular weights), then LDF usually dominate the interactions, and the larger molecules will have higher melting or boiling points, even if they are less polar.

What is an instantaneous dipole? Describe how it forms

a fleeting non uniform distribution of electron density in a molecule without a permanent dipole. -Let's consider two helium atoms in close proximity (Figure F11-4-2). On average, they have perfectly spherical electron density, but electrons are in constant motion which can result in both electrons being on the same side of the He nucleus at any one moment in time, yielding an instantaneous, if temporary, asymmetry of the electron distribution. -This instantaneous dipole moment can induce a temporary dipole moment in a second He atom, which happens to be in close proximity, and other neighboring atoms will be similarly affected.

What is an induced dipole? Explain how one is formed.

a temporary dipole created by a momentary uneven distribution of electrons in a molecule or atom. -An induced dipole moment is caused by a temporary shift in the electron cloud density.

What are the three states of matter? What are their differences in respect to intermolecular interactions and kinetic energy?

any of the three states of matter: gas, liquid, solid; also, one of two or more solid-state structures of the same substance, such as iron in a body-centered cubic or face centered cubic structure. -In gases thermal motions dominate, and in solids the intermolecular forces prevail, whereas in liquids the thermal motions and intermolecular forces are comparable.

non-ideal gas behavior

apparent deviations from the ideal gas behavior at -higher pressures, -decreasing volumes, -and decreasing temperature.

Give an example of dipole-dipole interactions.

attractive forces that act between polar molecules. Dipole-dipole = polar liquids or solids. CH3CN(ℓ) or (s)

What do we mean by dispersion forces?

attractive weak forces that act between all molecules, including nonpolar molecules, resulting from the formation of instantaneous dipoles and induced dipoles.

Using F12-2-1, find ump, uav and urms for different molecules at the same temperature (300 K). (The default figure will be for O2, H2O, He and H2). Which of the four has the greatest urms? What is the relationship between rms speed and the molar mass of a gas at constant T?

next

Using Figure 13-2-1, describe what line BC represents. What equation is used to calculate the amount of heat absorbed from point B to point C?

not certain

What does the line AB represent in Figure 13-2-1? What equation is used to calculate the heat absorbed from point A to point B?

not certain

How do we calculate the amount of heat needed to change the temperature of a pure substance?

q = n Cm ΔT = m Cs ΔT Cm = molar heat capacity if given per mole. Cs = specific heat capacity if given for 1 gram of the substance. -The amount of heat (q) needed to raise the temperature of n moles or m grams of a substance by a certain number of degrees of temperature. -In general, each phase of a substance has its own unique Cm, and Cs can be calculated by dividing Cm by the molecular weight.

Review: List four ways gases differ from liquids and solids. (See Chapter 11-1)

solid: Has a definite shape and volume. liquid: Has a definite volume, but take the shape of the container. gas: Has no definite shape or volume. change of state: When matter is converted from one of the three states (example: solid, liquid, or gas) to another state. References.

The temperature increasing indicates ...

the growing kinetic energy of the particles.

What is the definition of partial pressure?

the pressure that one gas in a mixture of gases would exert if it occupied the same volume at the same temperature as the mixture.

Describe the relationships derived from equation E12-1-4. (Hint: how are temperature and molar mass related to root mean square speed?)

urms = square root of {(3RT) / (M)} -all particles move faster at higher temperatures, and lighter particles move faster than heavier particles at the same temperature.

What does equation E12-1-2 tell us about the temperature of a collection of molecules?

ϵav = (3/2) x KB x T -Temperature is a measure of the average kinetic energy of particles.