Physical Science: B: Chemistry

Interpreting Chemical Equations

- tells you *relative amounts* of reactants and products - can be interpreted in terms of *number of atoms, molecules, or moles; mass; and volume

Catalysts

A catalyst is a species that speeds up a chemical reaction without being chemically changed upon completion of the reaction. In other words, the mass of a catalyst is the same before and after a reaction occurs.

Neutralization

A chemical reaction in which an acid and a base react quantitatively with each other. In a reaction in water, neutralization results in there being no excess of hydrogen or hydroxide ions present in the solution.

Solution

A homogeneous mixture of two or more substances uniformly dispersed throughout a single phase.

PH Scale

A range of values used to express the concentration of hydrogen ions in a solution.

Endothermic reaction

A reaction in which energy (heat) is absorbed.

Exothermic reaction

A reaction that releases energy in the form of heat.

Single Replacement

A single-displacement reaction, also known as a single-replacement reaction, is a type of chemical reaction where an element reacts with a compound and takes the place of another element in that compound. This type of reaction is typically pictured like this: Here, A replaces B in the compound BC.

Solute

A substance that is dissolved in a solution. • A solute is a substance in which is dissolved in another substance, the solvent. • A common example used to explain this is using salt water; salt dissolved in water. In that case, salt is the solute and water is the solvent. ... In other words, a solution is a homogeneous mixture, either liquid or soild.

Double replacement

A type of chemical reaction where two compounds react, and the positive ions (cation) and the negative ions (anion) of the two reactants switch places, forming two new compounds or products.

Covalent bonding

Also called a molecular bond, is a chemical bond that involves the sharing of electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs, and the stable balance of attractive and repulsive forces between atoms, when they share electrons, is known as covalent bonding.

Concentrated solution

An aqueous solution consists of at least two components, the solvent (water) and the solute (the stuff dissolved in the water). Usually one wants to keep track of the amount of the solute dissolved in the solution. We call this the concentrations.

Activation Energy

As the temperature increases, the molecules move faster and therefore collide more frequently. The molecules also carry more kinetic energy. Thus, the proportion of collisions that can overcome the activation energy for the reaction increases with temperature.

Litmus Paper vs. pH Strips

Both litmus paper and pH strips are small strips of paper coated with a chemical that will undergo a chemical change to a different color when it reacts with the chemical being tested. Litmus paper is either red or blue. Red litmus paper turns blue if it comes in contact with a base, alternatively blue litmus paper turns red with acids. This is a pass or fail type of test that only works with acidic or basic chemicals. Neutral solutions do not cause a color change. The strips work similarly, however, the color change occurs at the actual pH value of the substance being tested and there are more colors. For example, if you are testing a citrus juice, the color change would happen around the 1 or 2 pH level whereas water would change color around 7.

Boyle's Law

Boyle's Law describes the inverse proportional relationship between pressure and volume at a constant temperature and a fixed amount of gas. This law came from a manipulation of the Ideal Gas Law. P∝1V(1.4) or expressed from two pressure/volume points: P1V1=P2V2(1.5) This equation would be ideal when working with problem asking for the initial or final value of pressure or volume of a certain gas when one of the two factor is missing.

Charle's Law

Charles's Law describes the directly proportional relationship between the volume and temperature (in Kelvin) of a fixed amount of gas, when the pressure is held constant. V∝T(1.6) or express from two volume/temperature points: V1T1=V2T2(1.7) This equation can be used to solve for initial or final value of volume or temperature under the given condition that pressure and the number of mole of the gas stay the same.

Simple oxidation-reduction reactions

Comprised of two parts, a reduced half and an oxidized half, that always occur together. The reduced half gains electrons and the oxidation number decreases, while the oxidized half loses electrons and the oxidation number increases.

Dilute solution

Dilution is a reduction in the pH of a chemical (gas, vapor, solution). It is the process of decreasing the concentration of a solute in solution, usually simply by mixing with more solvent. To dilute a solution means to add more solvent without the addition of more solute.

Agitation

Dissolving sugar in water will occur more quickly if the water is stirred. The stirring allows fresh solvent molecules to continually be in contact with the solute. If it is not stirred, then the water right at the surface of the solute becomes saturated with dissolved sugar molecules, meaning that it is more difficult for additional solute to dissolve. The sugar cube would eventually dissolve because random motions of the water molecules would bring enough fresh solvent into contact with the sugar, but the process would take much longer. It is important to realize that neither stirring nor breaking up a solute affect the overall amount of solute that dissolves. It only affects the rate of dissolving.

Periodic Table of the elements

Elements in the periodic table are arranged in groups and periods. Elements in the periodic table are arranged in periods (rows) and groups (columns). Atomic number increases as you move across a row or period. Rows of elements are called periods.

Freezing point depression

Freezing-point depression. ... Freezing-point depression is the process in which adding a solute to a solvent decreases the freezing point of the solvent. Examples include salt in water, alcohol in water, or the mixing of two solids such as impurities in a finely powdered drug.

Amonton's Law

Given a constant number of mole of a gas and an unchanged volume, pressure is directly proportional to temperature. P∝T(1.10) or expressed as two pressure/temperature points: P1T1=P2T2(1.11)

Temperature (dissolving)

Heating up the solvent gives the molecules more kinetic energy. The more rapid motion means that the solvent molecules collide with the solute with greater frequency and the collisions occur with more force. Both factors increase the rate at which the solute dissolves. As we will see in the next section, a temperature change not only affects the rate of dissolving, but also affects the amount of solute that dissolves. The higher the temperature, the faster the rate of dissolving for a solid in a liquid. Particle size (effect on surface area)

The Gas Constant

Here comes the tricky part when it comes to the gas constant, R. Value of R WILL change when dealing with different unit of pressure and volume (Temperature factor is overlooked because temperature will always be in Kelvin instead of Celsius when using the Ideal Gas equation). Only through appropriate value of R will you get the correct answer of the problem. It is simply a constant, and the different values of R correlates accordingly with the units given. When choosing a value of R, choose the one with the appropriate units of the given information (sometimes given units must be converted accordingly). Here are some commonly used values of R:

Isotopic abundance

In physics, natural abundance (NA) refers to the abundance of isotopes of a chemical element as naturally found on a planet. The relative atomic mass (a weighted average, weighted by mole-fraction abundance figures) of these isotopes is the atomic weight listed for the element in the periodic table. • Elements can have different masses, which is due to the number of neutrons. However, they are chemically the same because that depends on the number of protons (atomic number). These care called isotopes i.e. U-233, U-235, U-238, etc. They are all uranium, but differ in neutron number. Isotopic abundance is how much of a given element is a particular isotope i.e. how much of the Uranium is actually U-235 and not say U-236,U-237,U-238.

Concentration

In terms of the collision theory, increasing the concentration of a reactant increases in the number of collisions between the reacting species per second and therefore increases the reaction rate.

Ionic bonding

Ionic bonding is the complete transfer of valence electron(s) between atoms. It is a type of chemical bond that generates two oppositely charged ions. In ionic bonds, the metal loses electrons to become a positively charged cation, whereas the nonmetal accepts those electrons to become a negatively charged anion

• Le Chatelier's principle

Le Chatelier's Principle and explains how to apply it to reactions in a state of dynamic equilibrium. It covers changes to the position of equilibrium if you change concentration, pressure or temperature. It also explains very briefly why catalysts have no effect on the position of equilibrium. • If a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium moves to counteract the change.

Effect of temperature and pressure on solubility (e.g., solubility curves)

Liquids and solids exhibit practically no change of solubility with changes in pressure. Gases as might be expected, increase in solubility with an increase in pressure. Henry's Law states that: The solubility of a gas in a liquid is directly proportional to the pressure of that gas above the surface of the solution.

Avogadro's number

Number of units in one mole of any substance (defined as its molecular weight in grams), equal to 6.022140857 × 10 23. The units may be electrons, atoms, ions, or molecules, depending on the nature of the substance and the character of the reaction (if any).

Atomic radius

One-half the distance between the nuclei of identical atoms that are bonded together.

Precipitation

Precipitation is the creation of a solid from a solution. When the reaction occurs in a liquid solution, the solid formed is called the 'precipitate'. The chemical that causes the solid to form is called the 'precipitant'.

Pressure (dissolving)

Pressure, causes the solute to be increased in the solvent, because the pressure forces the remaining gases into the solute. Therefore, pressure increases the solubility, and also changes the reaction rate. Finally, the surface area exposed to the solvent determines the rate of which a solute will dissolve.

Gramps per liter

Simply the mass of a solute in grams dissolved in a given volume of solution. Usually used for solutions made from solid solutes and liquid solvents, like our sugar and vinegar example.

Standard Temperature and Pressure (STP)

Standard condition of temperature and pressure is known as STP. Two things you should know about this is listed below. • The universal value of STP is 1 atm (pressure) and 0o C. Note that this form specifically stated 0o C degree, not 273 Kelvin, even thought you will have to convert into Kelvin when plugging this value into the Ideal Gas equation or any of the simple gas equations. • In STP, 1 mole of gas will take up 22.4 L of the volume of the container.

Temperature

Temperature (in Kelvin degrees) is proportional to the kinetic energy of the particles in a substance. For example, if the Kelvin temperature of a substance is doubled, then the average kinetic energy of the particles in that substance is doubled. At higher temperatures, particles collide more frequently and with greater intensity.

Ionization energy

The amount of energy required to remove an electron from an atom.

Pressure

The concentration of a gas is a function of the pressure on the gas. Increasing the pressure of a gas is exactly the same as increasing its concentration. If you have a certain number of gas molecules, you can increase the pressure by forcing them into a smaller volume.

Solvent

The dissolving agent of a solution. Water is the most versatile solvent known.

Factors that affect reaction equilibrium

The factors that can influence equilibrium are change in concentration, change in pressure (or volume), and change in temperature. First, the reaction must be at equilibrium. Let's add more N2O4 as an illustration of a change in concentration. The concentration of N2O4 increases, and the equilibrium is disturbed.

Atomic mass

The mass of an atom of a chemical element expressed in atomic mass units. It is approximately equivalent to the number of protons and neutrons in the atom (the mass number) or to the average number allowing for the relative abundances of different isotopes.

Molar Mass

The molar mass is the mass of a given chemical element or chemical compound (g) divided by the amount of substance (mol). The molar mass of a compound can be calculated by adding the standard atomic masses (in g/mol) of the constituent atoms.

Acid - Base Indicators

The most common method to get an idea about the pH of solution is to use an acid base indicator. An indicator is a large organic molecule that works somewhat like a " color dye". Whereas most dyes do not change color with the amount of acid or base present, there are many molecules, known as acid - base indicators , which do respond to a change in the hydrogen ion concentration. Most of the indicators are themselves weak acids. The most common indicator is found on "litmus" paper. It is red below pH 4.5 and blue above pH 8.2. Other commercial pH papers are able to give colors for every main pH unit. Universal Indicator, which is a solution of a mixture of indicators is able to also provide a full range of colors for the pH scale. A variety of indicators change color at various pH levels. A properly selected acid-base indicator can be used to visually "indicate" the approximate pH of a sample. An indicator is usually some weak organic acid or base dye that changes colors at definite pH values. The weak acid form (HIn) will have one color and the weak acid negative ion (In-) will have a different color. The weak acid equilibrium is: HIn --> H+ + In- For phenolphthalein: pH 8.2 = colorless; pH 10 = red For bromophenol blue: pH 3 = yellow; pH 4.6 = blue See the graphic for more indicators, colors, and pH ranges.

Naming compounds based on formulas

The names for ionic compounds are very simple. The first part of the name is simply the name of the metal element. The second part of the name is the name of the nonmetal element, with the ending changed to the suffix -ide. For example, consider the compound Al2O3.

Molarity

The number of moles of a solute divided by the volume of the solution.

Atomic number

The number of protons in the nucleus of an atom, which determined the chemical properties of an element and its place in the periodic table.

Particle Size

The smaller the size of the particles, the faster they dissolve.

Percent composition

To calculate percent by mass, you need to determine two things: the mass of just the element, and the molar mass of the whole compound. Then, you take the molar mass of just the element and divide it by the molar mass of the whole compound, and multiply by 100%.

Combustion

Usually occurs when a hydrocarbon reacts with oxygen to produce carbon dioxide and water. In the more general sense, combustion involves a reaction between any combustible material and an oxidizer to form an oxidized product. A combustion reaction is when oxygen combines with another substance to produce waer and carbon dioxide. These reactions are exothermic. (wood burning)

Avogardo's Law

Volume of a gas is directly proportional to the amount of gas at a constant temperature and pressure. V∝n(1.8) or expressed as a two volume/number points.

Unsaturated solution

When the solute CANNOT dissolve into the solvent. For example, if you have a glass of water, and you pour something like vegetable oil into it, it will not dissolve. So that makes the solution unsaturated

Supersaturated solution

When you pour the solute into the solvent and the solute doesn't dissolve. For example, if you have cup of iced tea, and you pour sugar into the tea, it is supersaturated when the sugar settles on the bottom of the glass. If you were to take the ice out of the tea, the sugar could then dissolve.

Non-polar solvents

contain bonds between atoms with similar electronegativities, such as carbon and hydrogen (think hydrocarbons, such as gasoline)

Polar solutes

dissolve in polar solvents, forming polar bonds or hydrogen bonds.

Polar solvents

have large dipole moments (aka "partial charges"); they contain bonds between atoms with very different electronegativities, such as oxygen and hydrogen

Non-polar solutes

non-polar solutes dissolve better in non-polar solvents. • Because water is polar and oil is nonpolar, their molecules are not attracted to each other. The molecules of a polar solvent like water are attracted to other polar molecules, such as those of sugar. ... In general, polar solvents dissolve polar solutes, and nonpolar solvents dissolve nonpolar solutes.

Kinetic theory of matter

states that matter is composed of a large number of small particles—individual atoms or molecules—that are in constant motion. the theory that the minute particles of all matter are in constant motion and that the temperature of a substance is dependent on the velocity of this motion, increased motion being accompanied by increased temperature: according to the kinetic theory of gases, the elasticity, diffusion, pressure, and other physical properties of a gas are due to the rapid motion in straight lines of its molecules, to their collisions against each other and the walls of the container, to weak cohesive forces between molecules, etc. • No energy is gained or lost when molecules collide. • The molecules in a gas take up a negligible (able to be ignored) amount of space in relation to the container they occupy. • The molecules are in constant, linear motion. • In a gas, the separation between particles is very large compared to their size, such that there are no attractive or repulsive forces between the molecules. • In a liquid, the particles are still far apart, but now they are close enough that attractive forces confine the material to the shape of its container. • In a solid, the particles are so close that the forces of attraction confine the material to a specific shape.

Enzymes

• By increasing the enzyme concentration, the maximum reaction rate greatly increases. • Enzymes are biological catalysts. Catalysts lower the activation energy for reactions. The lower the activation energy for a reaction, the faster the rate. Thus enzymes speed up reactions by lowering activation energy.

Dissociation of ionic compounds such as salts in water (e.g., ionization, electrolytes)

• Dissociation in chemistry and biochemistry is a general process in which molecules (or ionic compounds such as salts, or complexes) separate or split into smaller particles such as atoms, ions or radicals, usually in a reversible manner. For instance, when an acid dissolves in water, a covalent bond between an electronegative atom and a hydrogen atom is broken by heterolytic fission, which gives a proton (H+) and a negative ion.

Effect of temperature, pressure, particle size, and agitation on the rate of dissolving

• We know that the dissolving of a solid by water depends upon the collisions that occur between the solvent molecules and the particles in the solid crystal. Anything that can be done to increase the frequency of those collisions and/or to give those collisions more energy will increase the rate of dissolving. Imagine that you were trying to dissolve some sugar in a glassful of tea. A packet of granulated sugar would dissolve faster than a cube of sugar. The rate of dissolving would be increased by stirring, or agitating the solution. Finally, the sugar would dissolve faster in hot tea than it would in cold tea.

Preparation of solutions of varying concentrations

• When preparing solutions, it is often easier to dilute an existing stock solution than it is to weigh out a solid solute and then dissolve it in the solvent. This is especially true if you want to prepare several solutions that each have a different concentration of the same solute. • One way to dilute an existing stock solution is by using the parallel dilution technique. When using this technique, first calculate the amount of stock solution needed to make your dilution.