Chemistry 115 Midterm 1

What is chemical kinetics?

The study of the rate of change of concentrations of substances involved in chemical reactions.

What factors affect reaction rates?

1. Physical state of reactants

2. Concentration of reactants

3. Temperature

4. Presence of a catalyst.

What is the definition of average rate in chemical kinetics?

Change in concentration of reactant or product over a specific time interval.

How do you graphically determine the instantaneous reaction rate?

By finding the tangential slope of the concentration versus time plot.

What is a rate law?

An equation that defines the experimentally determined relationship between reactant concentrations and the rate of the reaction.

What is reaction order?

An experimentally determined number that defines the dependence of the reaction rate on the concentration of a reactant.

How is the rate constant (k) defined in a rate law?

It is a proportionality constant that relates the rate of a reaction to the concentrations of reactants.

What occurs in a first-order reaction with respect to the concentration?

The rate changes by the same factor as the concentration; doubling the initial concentration will double the rate.

How is the half-life of a first-order reaction characterized?

The half-life is independent of the initial concentration.

What is an activated complex in a chemical reaction?

A temporary, high-energy chemical species formed during a reaction when reacting molecules collide effectively (aka transition state)

What is the collision frequency factor in the Arrhenius equation?

The number of effective collisions per unit time needed for a reaction to occur.

What determines the rate determining step (RDS) in a reaction mechanism?

It is the slowest step that dictates the overall reaction rate.

What is a catalyst in a chemical reaction?

A substance that increases the speed of a reaction without undergoing permanent chemical change.

What does homogeneous catalysis refer to?

When the catalyst and the reactants are in the same phase.

What is the role of an enzyme in biological reactions?

Act as biocatalysts, facilitating reactions by lowering the activation energy and adsorbing substrates onto active sites.

How does increasing temperature generally affect reaction rates?

Increasing temperature usually increases reaction rates by doubling the speed of the reaction for every 10°C rise.

What is molecularity in the context of an elementary step?

The number of reactant particles involved in that step; unimolecular (1), bimolecular (2), or termolecular (3).

What is the effect of a catalyst on activation energy?

A catalyst provides an alternative mechanism with lower activation energy.

What happens during the forward reaction in a chemical equilibrium?

Reactants are converted into products, resulting in a decrease in reactant concentrations and an increase in product concentrations.

What is dynamic equilibrium?

Dynamic equilibrium is the condition where the rates of the forward reaction and reverse reaction are equal, leading to constant concentrations of reactants and products.

What does the equilibrium constant (K) represent?

K is the numerical value of the equilibrium constant expression of a reversible chemical reaction at a particular temperature.

How is the equilibrium constant expression derived according to the Law of Mass Action?

It is the ratio of the equilibrium concentrations or partial pressures of products to reactants, with each term raised to the power equal to its coefficient in the balanced equation.

What does a large value of Keq (Keq >> 1) indicate about a reaction?

It indicates that there will be many more product molecules present than reactant molecules at equilibrium, favoring products.

What does a small value of Keq (Keq << 1) indicate about a reaction?

It indicates that there will be many more reactant molecules present than product molecules at equilibrium, favoring reactants.

What happens to the equilibrium constant if the equation is reversed?

The equilibrium constant is inverted.

If the coefficients in a balanced equation are multiplied by a factor, what happens to K?

The equilibrium constant is raised to the same factor.

Are pure solids and liquids included in the equilibrium constant expression?

No, pure solids and liquids are not included because their concentrations do not change during the reaction.

What relationship exists between Kp and Kc at constant temperature?

Kp = Kc(RT)∆n, where ∆n is the change in moles of gas between products and reactants.