Chem II Kinetics / Rate law

The average rate is described by which of the following?

The average rate is the rate of a chemical reaction computed as the ratio of a measured change in amount or concentration of substance to the time interval over which the change occurred.

Which of the following gives the definition of initial rate?

The initial rate is defined as the instantaneous rate of a chemical reaction immediately after the reaction has begun.

The term rate of reaction is best described by which of the following?

The rate of reaction is a measure of the speed at which a chemical reaction takes place. The rate of reaction is defined as the measure of the speed at which a chemical reaction takes place.

Which is an example of concentration affecting the rate of reaction?

a solution containing two moles of each reactant has a faster instantaneous rate of reaction than a solution of the same volume with only one mole of each reactant These solutions clearly have differing concentrations of reactants, and they will therefore exhibit differing initial rates.

For the following reaction, to get the rate of consumption of O2, what must we multiply the rate of consumption of NH3 by? 4NH3+5O2→4NO+6H2O

5/4 These are both reactants, so if one is being consumed, than the other will also be consumed, so the factor will be positive, not negative. Since, from the coefficients, there are 5 O2 molecules per 4 NH3 molecules, the factor will be 5/4. This is called the stoichiometric ratio.

Which is an example of concentration affecting the rate of reaction?

A reaction slows down as it proceeds. As a reaction proceeds, the concentrations change, and as the concentration of reactants is reduced, the reaction will go more slowly.

Identify the option below that increases the rate of a reaction.

Allowing some solvent to evaporate from the vessel containing a reaction that takes place entirely in solution Increasing the concentration of reactants in a reaction solution will generally speed the reaction up.

Which of the following decreases the rate of a reaction?

Decreasing the amount of a first order solid reactant The amount of a first order reactant affects the reaction rate; hence, removing some of this solid will slow the reaction down.

Identify the options below that decrease the rate of a reaction. (select all that apply)

Decreasing the temperature of an endothermic reaction Decreasing the concentration of a second order reactant

A rate expression for any reactant of a chemical reaction will always be:

Negative

Which of the following is an example of reactant concentration affecting the rate of a reaction?

Phosphorus burns much more rapidly in an atmosphere of pure oxygen than in air, which is about 21% oxygen. The rate of a reaction usually increases when the concentration of one or more of the reactants increases.

All of the following are examples of the temperature of reactants affecting the rate of a reaction except:

Phosphorus burns much more rapidly in an atmosphere of pure oxygen than in air. Each of these examples illustrates how a change in temperature affects the rate of a reaction except the last. The last example deals with the effect of reaction concentration instead.

A rate expression for any product of a chemical reaction will always be:

Positive

The conductivity of the solution in a reaction can be used to measure rates of reactions involving:

aqueous electrolytes The conductivity of a solution containing reactive electrolytes can be used to measure the rate of reaction, since electrolytes conduct electricity.

In general, as a reaction proceeds:

concentrations and rates both change

The rate at which a reaction is proceeding at a specific point in time is called the:

instantaneous rate At any particular instant, a reaction will be proceeding at an instantaneous rate that is unique to that moment.

What term is best described as the rate of a chemical reaction at any instant in time?

instantaneous rate The instantaneous rate is defined as the rate of a chemical reaction at any instant in time.

A catalyst lowers the activation energy of a reaction by:

providing an alternate pathway or mechanism Any catalyst will somehow offer an alternate pathway or mechanism for a reaction than would otherwise occur without the catalyst.

The mathematical expression of change in concentration over time is called the:

rate expression A rate expression shows the change in concentration over change in time for a particular substance in a chemical reaction.

A catalyst will:

reduce the activation energy of a reaction A catalyst lowers the activation energy of a reaction, while leaving the change in enthalpy unaffected.

If concentration and time are plotted graphically, the rate of the reaction at any particular time can be found by looking at the:

slope of the tangent line The slope of the tangent line at any particular point will give the rate of the reaction at that particular time.

As a reaction proceeds, the ratio between the rate of consumption of reactant and the rate of formation of product:

stays the same While the concentrations and rates change, the ratio between the rates stays the same, as it must obey the stoichiometric ratios.

An increase in temperature of ten degrees Celsius will have what effect on the rate?

the rate will approximately double An increase in temperature will speed up most chemical processes. For many chemical processes, reaction rates are approximately doubled when the temperature is raised ten degrees Celsius.

When is the average rate of a reaction equal to its instantaneous rate at a given second?

when the reaction proceeds at a constant rate If the rate of a reaction is constant, a graph of reactant amount vs. time will be a straight line: the tangent to this line will simply be the line itself. For this type of reaction, therefore, the instantaneous rate is equal to the average rate.