Chemistry Reactions and Rates Quiz

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Questions and Answers

What can be used to prevent a catalyst or a reactant from reacting?

Poisonous compounds like cyanide (correct)

A reactant that increases pressure

High temperatures

Concentration of gaseous reactants

Which factor primarily affects the rate of heterogeneous reactions?

Surface area (correct)

Temperature

Concentration of reactants

Pressure

What effect does increasing the surface area have on a solid reactant?

It accelerates the reaction rate. (correct)

It slows down the reaction rate.

It changes the phase of the reactant.

It has no effect on the reaction rate.

Which statement is true regarding gaseous reactants?

They are usually faster to react than solids. Signup and view all the answers

What impact does temperature have on reaction rates?

It affects the rate of all reactions. Signup and view all the answers

What is the primary reason for measuring mass changes in reactions involving solids?

To track the consumption of a single solid reactant Signup and view all the answers

In the reaction of solid magnesium with hydrochloric acid, which component's mass would decrease if magnesium is periodically removed?

Mass of magnesium Signup and view all the answers

Which of the following statements about measuring ionic concentrations is true?

Concentration can be monitored by titration of periodic samples. Signup and view all the answers

What effect does the reaction between magnesium and hydrobromic acid have on the concentration of hydrogen ions?

The concentration of hydrogen ions decreases. Signup and view all the answers

Why is it impractical to measure the masses of aqueous substances separately?

Aqueous substances are mostly water, complicating the measurement. Signup and view all the answers

In a reaction producing gas, how can the mass change be measured accurately?

By subtracting the initial mass from the final mass of the container and contents Signup and view all the answers

What is the impact of a spectator ion on the overall reaction rate?

It does not change the concentration during the reaction. Signup and view all the answers

What is indicated by the rate of a reaction involving changes in molar concentration?

The speed at which reactants are transformed into products Signup and view all the answers

What is the correct formula to express the rate of a reaction?

rate = Δ amount / Δ time Signup and view all the answers

In a reaction, if 20 g of H2SO4 are consumed in 16 minutes, what is the average reaction rate?

0.833 g/min Signup and view all the answers

What color change occurs when Cu(NO3)2 is reacted with Zn?

The blue color fades as reaction progresses Signup and view all the answers

When converting grams of Mg to moles, what must you consider?

The molar mass of Mg Signup and view all the answers

What happens to the temperature in an exothermic reaction?

The temperature of the surroundings increases Signup and view all the answers

How do you represent a reaction in ionic form?

Dissociate all aqueous compounds Signup and view all the answers

In a sealed container, what effect does an increase in moles of gas in the products have on pressure?

Pressure will increase Signup and view all the answers

What would be a correct approach to compare rates using a balanced equation?

Use coefficient ratios based on moles Signup and view all the answers

If the reaction rate of Mg is 0.034 g/s, how many grams would be used in 6 minutes?

12.24 g Signup and view all the answers

When considering the pressure changes in a reaction at constant volume, what establishes whether pressure will change?

The number of moles of gas in the reactants versus products Signup and view all the answers

In a reaction producing 4CO2 and 6H2O from 2C2H6 and 7O2, how many moles of CO2 are produced per mole of C2H6 consumed?

4 moles Signup and view all the answers

What can be used to quantitatively measure the color intensity of a reaction?

A spectrophotometer Signup and view all the answers

Which of the following is true regarding the time units in a rate equation?

Time units are always in the denominator. Signup and view all the answers

What occurs to the volume of a balloon when more gas is produced in a reaction at constant pressure?

The volume will increase Signup and view all the answers

What is the net ionic equation of the reaction between Cu(NO3)2 and Zn?

Cu(aq) + Zn(s) → Zn(aq) + Cu(s) Signup and view all the answers

In the example of NO2 and CO reacting, what is the change in pressure observed when equal moles of gas are present in reactants and products?

Pressure will not change Signup and view all the answers

What is a reaction intermediate?

A species that is formed and used up in a reaction. Signup and view all the answers

Which statement accurately describes the activated complex?

It is a very unstable and short-lived structure. Signup and view all the answers

What does a higher bump in a potential energy diagram indicate?

A higher activation energy for the step. Signup and view all the answers

What does the vertical distance from reactants to the highest peak in a potential energy diagram represent?

The activation energy for the forward overall reaction. Signup and view all the answers

In a reaction mechanism, what can be said about intermediates?

They are formed in one step and consumed in another. Signup and view all the answers

What will always be true about the rate-determining step (RDS) in a reaction mechanism?

It occurs at the highest energy level. Signup and view all the answers

Which step would be considered the fastest step in a reaction mechanism?

The step with the lowest activation energy. Signup and view all the answers

What would characterize an exothermic reaction in terms of the potential energy diagram?

The energy of products is lower than that of reactants. Signup and view all the answers

What effect does a catalyst have on the activation energy of a reaction?

It lowers the activation energy. Signup and view all the answers

In a catalyzed reaction, how does the energy required for the reverse reaction compare to the uncatalyzed reaction?

It is lower than the activation energy of the uncatalyzed reaction. Signup and view all the answers

Which statement is true regarding the change in potential energy (PE) of reactants and products when a catalyst is introduced?

The PE of reactants and products remains unchanged. Signup and view all the answers

What is the typical effect of a catalyst on the overall reaction mechanism?

It usually involves more steps with a lower activation energy. Signup and view all the answers

What is implied by an overall exothermic reaction in terms of reaction energy?

The energy of products is lower than that of reactants. Signup and view all the answers

In a potential energy diagram for a two-step reaction mechanism, which step is characterized as being fast?

The first step of the mechanism. Signup and view all the answers

If a catalyst is added to a system with an uncatalyzed reaction, what happens to the uncatalyzed reaction?

It continues at its own slow rate. Signup and view all the answers

What is the role of a catalyst in the context of providing an alternative mechanism?

To allow the reaction to proceed with a lower activation energy. Signup and view all the answers

Study Notes

Introduction to Reaction Kinetics

Reaction kinetics is the study of reaction rates and factors affecting those rates.
Reaction rate is defined as the amount of reactant or product over time.
Time units are always in the denominator of the rate equation.

Calculations Involving Reaction Rates

Use molar mass to convert between grams and moles.
Use 22.4 L/mol for gas conversions at standard temperature and pressure (STP).
Ensure units cancel out correctly when converting.
Follow the general approach of writing a plan for calculations.

Comparing Rates Using Balanced Equations

Use ratios of coefficients in a balanced equation.
Use mol/s, not g/s when comparing rates of consumption or production.

Methods of Measuring Reaction Rates

Properties monitored to determine reaction rates include:
- Color changes (intensity measured with a spectrophotometer)
- Temperature changes (measured in a calorimeter)
- Pressure changes (constant volume)
- Volume changes (constant pressure)
- Mass changes
- Changes in molar concentration of specific ions
- Changes in pH

Factors Affecting Reaction Rates

Temperature: Higher temperatures generally increase reaction rates.
Concentration: Higher concentrations generally increase reaction rates (more likely collisions with adequate energy)
Nature of reactants: Strong bonds are generally harder to break, resulting in slower reactions
Pressure: Increased pressure affects reactions with gases, increasing rates.
Surface area: Increasing surface area generally increases reaction rate
Catalyst: Adding a catalyst speeds up reactions by lowering activation energy.

Reaction Rates and Collision Theory

Reactions require collisions between molecules with sufficient kinetic energy to break bonds and form new ones.
Increased temperature means higher average kinetic energy among molecules leading to more collisions per unit time.
Concentration of reactants influences the chance of collisions, increasing with more reactants.
The number and kinds of bonds affect reaction time

Enthalpy Changes in Chemical Reactions

Enthalpy (H) is heat content of a substance.
Enthalpy change (ΔH) is the heat absorbed or released in a reaction at constant pressure.
In an exothermic reaction, ΔH is negative (heat released).
In an endothermic reaction, ΔH is positive (heat absorbed)

Kinetic Energy Distributions

Different molecules have different kinetic energies.
A distribution curve shows the relative number of molecules with specific kinetic energy values.
- High energy molecules react faster
- Increases in temperature increase the fraction of high-energy molecules
The distribution curves' total area under the curve does not change

Activation Energies

Activation energy (Ea) is the minimum energy molecules need for a collision to result in a reaction.
Activation energy is influenced by reaction nature
Adding a catalyst lowers the activation energy required, increasing the reaction rate

Reaction Mechanisms

Reaction mechanisms are the steps involved in chemical reactions.
Intermediates are formed during the process.
The slowest step in the reaction mechanism is known as the rate-determining step, which is the rate limiting step and represents the overall limiting step of the reaction rate
Catalysts work by creating alternate pathways with lower activation energy.

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Description

Test your understanding of factors affecting reaction rates, including the role of catalysts, surface area, and temperature. This quiz covers key concepts in the study of chemical kinetics and heterogeneous reactions. Enhance your knowledge of how different conditions influence the effectiveness of reactants.