Chemistry Reaction Rates Quiz

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Questions and Answers

What does the average rate of a reaction depend on?

Pressure exerted during the reaction

Change in concentration of reactants or products and the time taken (correct)

Volume of the reaction mixture

Temperature changes in the environment

What are the units of the rate of a reaction when concentration is expressed in mol L–1 and time in seconds?

mol L–1 min–1

atm L–1 min–1

atm L–1 s–1

mol L–1 s–1 (correct)

When calculating the average rate of a reaction, what mathematical operation is used with the changes in concentration and time?

Division of the change in concentration by the change in time (correct)

Multiplication of concentration change by time

Subtraction of time from concentration change

Addition of concentration and time

In gaseous reactions, how is the concentration expressed to determine the rate of reaction?

Using partial pressures Signup and view all the answers

What is the average rate of a reaction if the change in concentration of a reactant over 100 seconds is 0.010 mol L–1?

0.010 mol L–1 s–1 Signup and view all the answers

What does the rate constant depend on according to the Arrhenius equation?

The activation energy and temperature Signup and view all the answers

What is the order of a reaction with respect to a reactant determined by?

The power of its concentration in the rate law equation Signup and view all the answers

What does the slope of the plot of ln k vs 1/T represent?

The activation energy divided by the gas constant Signup and view all the answers

Which statement about molecularity is correct?

Molecularity values are always whole numbers. Signup and view all the answers

What happens to the rate of a reaction when the temperature increases by 10K?

The rate doubles Signup and view all the answers

When subtracting equation (3.20) from equation (3.21), what do you obtain?

ln k2 - ln k1 = (Ea/R)(1/T1 - 1/T2) Signup and view all the answers

How is the average rate of a reaction defined?

Change in concentration over a long time interval Signup and view all the answers

What remains constant for a given reaction in the provided equations?

The pre-exponential factor A Signup and view all the answers

At higher temperatures, what is expected to happen to the rate constant based on the Arrhenius equation?

It increases exponentially Signup and view all the answers

In the example provided, what is the value of k1 at 500K?

0.02 s–1 Signup and view all the answers

Which of the following does not affect the rate of a chemical reaction?

Speed of retracing steps Signup and view all the answers

Which equation correctly relates k1 and k2 using the temperature terms?

log(k2/k1) = (Ea/R)(1/T2 - 1/T1) Signup and view all the answers

In a reaction, what is the relationship between rate constant and activation energy?

Rate constant decreases as activation energy increases Signup and view all the answers

What is the significance of the term 'threshold energy' in a chemical reaction?

It is the minimum energy required for a reaction to occur Signup and view all the answers

What does decreasing the activation energy result in according to the Arrhenius equation?

An increased reaction rate Signup and view all the answers

For the reaction 2HI(g) → H2(g) + I2(g), how is the rate of the reaction expressed?

Rate = $\frac{\Delta [HI]}{2 \Delta t}$ Signup and view all the answers

What does the parameter Ea represent in the context of chemical reactions?

The activation energy for a reaction Signup and view all the answers

How does the presence of a catalyst affect the activation energy in a chemical reaction?

It lowers the activation energy Signup and view all the answers

In the modified Arrhenius equation, what does the steric factor P account for?

The orientation of colliding molecules Signup and view all the answers

Given the rate expression rate = k[NO]², what is the order of the reaction with respect to NO?

Second order Signup and view all the answers

What is the unit of the rate constant k for a reaction where the rate is given as mol L⁻¹ s⁻¹ and the reaction is second order?

mol L⁻² s⁻¹ Signup and view all the answers

When [A] is 0.1 mol L⁻¹ and [B] is 0.2 mol L⁻¹ in the reaction 2A + B → A2B, what is the initial rate of the reaction if k = 2.0 × 10⁻⁶ mol⁻² L² s⁻¹?

4.0 × 10⁻⁶ mol L⁻¹ s⁻¹ Signup and view all the answers

What is the instantaneous rate of hydrolysis of butyl chloride at t = 600 s?

$5.12 \times 10^{-5}$ mol L$^{-1}$ s$^{-1}$ Signup and view all the answers

Which term in the equation ln k = -Ea/(RT) + ln A represents the constant factor for the reaction?

ln A Signup and view all the answers

In the reaction Hg(l) + Cl2(g) → HgCl2(s), what can be said about the rates of the reactants and products?

The rates of both reactants are equal to the rate of formation of the product. Signup and view all the answers

What is represented by the variable rinst in the context of chemical reactions?

The instantaneous rate of reaction at a specific moment Signup and view all the answers

When two moles of a reactant decompose to form products in a reaction, what must be considered to express the rate correctly?

The stoichiometric coefficients of the reactants and products Signup and view all the answers

If the instantaneous rate of HI decomposition is at a certain moment, what must be true regarding H2 and I2?

Their rates are half the rate of HI disappearance. Signup and view all the answers

At what concentration does the instantaneous rate of butyl chloride hydrolysis equal $1.0 \times 10^{-4}$ mol L$^{-1}$ s$^{-1}$?

At t = 350 s Signup and view all the answers

What is the significance of the pre-exponential factor A in the Arrhenius equation?

It relates to the collision frequency of particles Signup and view all the answers

How can the instantaneous rate be determined graphically for a reaction?

By finding the slope of the tangent at a specific time on the curve Signup and view all the answers

In a zero order reaction involving the decomposition of NH3, what remains constant regardless of the concentration of reactants?

Rate of reaction Signup and view all the answers

Study Notes

Rate of a Reaction

The rate of a reaction can be defined as the change in concentration of reactants or products per unit time.
The average rate is calculated over a large interval of time, while the instantaneous rate is calculated at a specific moment in time.
The units for the rate of a reaction are concentration time–1. For instance, if the concentration is in mol L–1 and time is in seconds, the units would be mol L–1s–1.
When dealing with gaseous reactions and the concentration of gases is expressed in terms of partial pressures, the units of the rate equation will be atm s–1.

Factors Affecting Rate of a Reaction

Temperature: Increasing temperature generally leads to a faster reaction rate.
Concentration of Reactants: Greater concentration of reactants typically results in a faster reaction rate.
Catalyst: Catalysts speed up a reaction without being consumed themselves.
Surface Area: For reactions involving solids, increasing surface area usually leads to an increased reaction rate.

Rate Law

The mathematical representation of the rate of a reaction is given by the rate law.
The rate law is an experimentally determined equation that shows how the rate of a reaction depends on the concentrations of the reactants.
It cannot be predicted theoretically.

Order of a Reaction

The order of a reaction with respect to a reactant is the power of that reactant's concentration in the rate law equation.
The overall order of a reaction is the sum of the orders with respect to each reactant.

Rate Constant

The rate constant, denoted by 'k', is a proportionality factor in the rate law.
It represents the rate of the reaction when the concentrations of all reactants are 1.
The rate constant is a specific value for a given reaction at a given temperature.

Molecularity

Molecularity refers to the number of molecules that participate in an elementary reaction step.
It is only defined for elementary reactions, which are the individual steps of a complex reaction.
The values of molecularity are usually limited to 1, 2, or 3, corresponding to unimolecular, bimolecular, and termolecular reactions, respectively.

Arrhenius Equation

The Arrhenius equation describes the temperature dependence of the rate constant.
k = Ae–Ea/RT
- k: Rate constant
- A: Arrhenius factor (pre-exponential factor)
- Ea: Activation energy
- R: Gas constant
- T: Temperature
The equation shows that increasing temperature or decreasing the activation energy leads to an increase in the reaction rate and an exponential increase in the rate constant.

Collision Theory

Collision theory suggests that for a reaction to occur, reactant molecules must collide with sufficient energy and proper orientation.
The activation energy (Ea) is the minimum energy required for a collision to be effective.
The frequency of collisions is influenced by factors such as temperature and concentration.
The steric factor (P) accounts for the probability of collisions having the correct orientation for a reaction.
The Arrhenius equation is modified to incorporate the steric factor: k  P Z ABe  E a / RT

Threshold Energy

Threshold energy is the minimum energy required for a reaction to occur.
It is the sum of the activation energy and the energy possessed by the reacting species.

Instantaneous Rate

Instantaneous rate is determined at a specific moment in time and can be determined by drawing a tangent to the concentration vs. time curve at that point.
The slope of the tangent represents the instantaneous rate.

Summary

Chemical kinetics is the area of chemistry that studies reaction rates and the factors that influence them.
Key factors influencing reaction rates include temperature, concentration, catalysts, and surface area.
The rate law expresses the mathematical relationship between the rate and reactant concentrations.
The order of a reaction describes how changes in reactant concentration affect the rate.
The rate constant reflects the specific rate of a reaction under given conditions.
Molecularity refers to the number of molecules involved in an elementary reaction step.
The Arrhenius equation relates the rate constant to temperature and activation energy.
Collision theory explains the basis for the energy requirement of reactions.
The threshold energy is the minimum energy needed for a reaction to occur and is the sum of the activation energy and the energy of the reactant molecules.

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Description

Test your understanding of the rate of reactions, including factors that affect it such as temperature, concentration, catalysts, and surface area. This quiz will challenge your knowledge of both average and instantaneous rates of reactions in chemistry. Perfect for students studying chemical kinetics!