Exam 2

The reaction A→B has been experimentally determined to be second order. The initial rate is 0.0100 M/s at an initial concentration of A of 0.100 MM.

0.360 M/s

The table in the notes that shows the rate law, units of k and the integrated rate law equations would be a great thing to put on a note card to use during a test.

True

When the reaction is multiplied by a factor, the new K is the "original K" raised to the power of the factor.

True

The half-life of a reaction is the __________ required for the ____________ of a reactant to fall to one-half of its initial value.

time; concentration

For the reaction A+2B→CA+2B→C under a given set of conditions, the initial rate is 0.130 M/s: -What is Δ[B]/ΔtΔ[B]/Δt under the same conditions?

-.260 M/s

A particular reaction, A → products, has a rate that slows down as the reaction proceeds. The half-life of the reaction is found to depend on the initial concentration of A. Determine whether each statement is likely to be true or false for this reaction. -A doubling of the concentration of A doubles the rate of the reaction. -A plot of 1/[A] versus time is linear. -The half-life of the reaction gets longer as the initial concentration of A increases. -A plot of the concentration of A versus time has a constant slope.

-False -True -False -False

This is straight forward. What types of substances would not be included in writing an equilibrium constant expression?

-Solids and Liquids

A reaction in which A, B, and C react to form products is first order in A, second order in B, and zero order in C. -Identify the rate law for the rxn: -What is the overall order of the rxn: -By what factor does the reaction rate change if [A] is doubled (and the other reactant concentrations are held constant)? -By what factor does the reaction rate change if [B] is doubled (and the other reactant concentrations are held constant)? -By what factor does the reaction rate change if [C] is doubled (and the other reactant concentrations are held constant)? -By what factor does the reaction rate change if the concentrations of all three reactants are doubled?

-k[A][B]^2 -3 -> m + n +p -> 1 + 2 + 0 = 3 -2 -. 2 / 1 = 2 -4 -1 -8

For a particular reaction in which A→products, doubling the concentration of AA has no effect on the reaction rate. What is the order of the reaction?

0

The reaction X→ products is second order in X and has a rate constant of 0.035 M−1s−1.

0.18 M

At the beginning of a rxn, the concentration of the product is always ___________.

2

The average rxn rate can be determined if the concentration of a substance is known at ________ points of the rxn.

2

The balanced chemical equation for the synthesis of ammonia, the Haber process, is shown below. If the nitrogen gas is disappearing at a rate of 0.2 M / s, what is the rate at which ammonia is appearing at the same point in time?

4.0 M/s

A diatomic molecule (0.500 M) dissociates in a first-order reaction with a rate constant, k, of 0.0775 s−1. What is the half-life of this reaction?

8.94 s

Consider the reaction below: 2 A → 2 B + C If the rate of reaction is directly proportional to the concentration of A, this reaction is _____.

A first-order rxn

First order:

A plot of natural log of concentration of rxn versus time yields a straight line.

Which statement best explains why reaction rates generally increase with increasing temperature?

As temperature increases, an increased number of molecules have sufficient energy to surpass the activation barrier; therefore, more reactants are converted to products.

The _________ rate of the rxn is calculated for a time interval, whereas the _____________ rate of the rxn is the rate at any one point in time.

Average; instantaneous

In this method, the initial rate is measured by running the rxn several times with ____________ initial reactant concentrations to determine the effect of the ____________ on the ___________.

Different; concentration; rate

Zero Order Rxn:

Doubling concentration does nothing to rxn rate. Rate= [A]^0 = K

First Order Rxn:

Doubling concentration doubles rxn rate. Rate= [A]^1 = k[A]

Second Order Rxn:

Doubling concentration quadruples the rxn rate. Rate= k[A]^2

What is the term for when rates of the forward and reverse reactions occur at the same rate?

Dynamic equilibrium

When writing an equilibrium constant expression, the coefficients in a balanced equation are used as:

Exponents

The rate law is determined by the coefficients of the balanced equation.

False

Zero order:

Half-life of rxn gets longer as initial concentration is increased.

Second order:

Half-life of rxn gets shorter as initial concentration is increased.

As the concentration of the reactants decreases, the concentration of the products will __________.

Increase

You can determine the __________ rate by calculating the slope of the tangent to the ___________ curve at the point of interest.

Instantaneous; concentration vs time.

When the reaction is reversed, the new K is the _____ of the original.

Inverse

A student prepares a graph of the concentration of A versus time ([A]t versus time) for the reaction below. A → B + C The graph is a straight line with a negative slope. What can you conclude about the order of the reaction?

It is a zero-order reaction.

Can the rate of a chemical rxn be determined by the balanced equation only?

No

Label the position of the reactants and products and indicate the activation energy and enthalpy of reaction.

On the diagram, the reaction pathway proceeds from left to right. Therefore, the curve begins at the energy of the reactants and ends at the energy of the products. The difference between the energy of reactants and the maximum energy corresponds to the activation energy, whereas the difference between the energy of reactants and products is the enthalpy of the reaction.

The order of a rxn can be determined __________ by experiment, ____________ by the stoichiometry of the rxn.

Only; not.

When writing equilibrium constants, _____ concentrations are in the numerator.

Product

If the inverse of [A] vs time gives a straight line, then the reaction is

Second order

If the units of "k" were 1/M s, we would be able to determine that the rxn is:

Second order

Which statement is false?

The rate of a chemical rxn speeds up as the reactants form products.

Experimental data show that the rate law for the reaction 2 HgCl2(aq) + C2O4 2 -(aq) → 2 Cl-(aq) + 2 CO2(g) + Hg2Cl2(s) is: rate = k[HgCl2][C2O4 2 -]2 How will the rate of reaction change if the concentration of C2O4 2 - is tripled and the concentration of HgCl2 is doubled?

The rate will increase by a factor of 18

First order reaction:

The relationship between the rate and the concentration of the reactant is linear (i.e., the rate is directly proportional to [A]), so the reaction is a first-order reaction.

Identify rate for first order reaction:

The relationship between the rate of the reaction and the concentration of the reactant is as follows: rate=k[A]^n where k is a constant of proportionality called the rate constant and n is the reaction order. Since the reaction is a first-order reaction (n=1), the rate law is: rate=k[A]

Identify rates:

The units of a rate constant are: k===rate[A] s−1 For a second-order reaction: rate=k[A]^2

It is important to be strategic in comparing experimental data. When you have more than one reactant, you should find rxns to compare that have one of the reactants changing and the other remain the same.

True

K is the result of the concentrations of the reactants and the products.

True

Many times we will be able to eyeball the data determine order but we still need to be able to prove it with the math.

True

The examples in the text are using "clean and neat" data so the exponents used to solve for "n" will be clear if the proof work is correct:

True

The graph can be used to identify which integrated rate law to use to find the concentration of the reactant at a particular time in the reaction.

True

The overall order of a rxn is the sum of the exponents of the individual rate laws of the reactants.

True

When would a reaction favor products at equilibrium?

When K > 1

If a graph shows a straight line when plotting [A] vs time, then the reaction is

Zero order

If the units of "k" were M/s, we are able to determine that the rxn is:

Zero order

If we collect concentration and rate data that shows the rate remains the same with concentration changes, we can determine that the rxn is:

Zero order

For a reaction with multiple reactants (Rate=k[A]m[B]n), how is the overall order of the reaction defined?

m + n

When comparing different exothermic reactions at a given temperature, the rate of a reaction with a lower activation energy is greater than that of a reaction with a higher activation energy because the _______.

number of successful effective collisions is higher