Chemistry Chapter 12: Catalysts and Reactions

Questions and Answers

What defines autocatalysis in a chemical reaction?

A reaction that occurs spontaneously without any catalyst

A product that inhibits the reaction rate

One of the products serves as a catalyst for the reaction (correct)

The catalyst is consumed in the reaction

Which of the following accurately describes activation energy?

The total energy of all reactants

The energy that is transformed into product

The energy required for particles to collide effectively (correct)

The energy released during a reaction

What is a characteristic of an effective collision in a chemical reaction?

It has sufficient activation energy to form products (correct)

It takes place over an extended time frame

It results in no products being formed

It occurs at low energy levels

How does increasing the concentration of reactants influence the reaction rate?

It increases the reaction rate due to more frequent collisions Signup and view all the answers

In the context of the decomposition of hydrogen peroxide, what role does manganese dioxide play?

It serves as a catalyst to speed up the reaction Signup and view all the answers

What relationship exists between ΔH and the classification of a chemical reaction?

A positive ΔH indicates a reaction that releases heat Signup and view all the answers

Which process describes how a catalyst reduces activation energy?

By forming an alternative reaction pathway Signup and view all the answers

Which of the following methods can increase the rate of a reaction involving gases?

Increasing the concentration of the gaseous reactants Signup and view all the answers

What does the instantaneous rate of a reaction represent?

The change in concentration at a specific moment in time Signup and view all the answers

Which statement about the average rate of reaction is true?

It equals the total products produced divided by total time Signup and view all the answers

What is the primary characteristic of the unstable intermediate formed between a reactant and a catalyst?

It is a temporary species. Signup and view all the answers

What phenomenon occurs when one substance accumulates at the surface of another substance?

Adsorption Signup and view all the answers

How does the use of a finely divided or porous catalyst affect the speed of a reaction?

The reaction rate increases. Signup and view all the answers

Which of the following substances act as inhibitors by blocking active sites on a catalyst?

Catalytic poisons Signup and view all the answers

Which of the following is considered a classic example of a catalyst poison?

Tetraethyl lead Signup and view all the answers

Which three metals are primarily composed within the catalytic converter?

Platinum, palladium, and rhodium Signup and view all the answers

What happens to the rate of reaction when temperature is increased?

The rate of reaction increases. Signup and view all the answers

Which relationship exists between temperature and the rate of a reaction?

Exponential relationship Signup and view all the answers

How is the instantaneous rate of reaction calculated?

By drawing a tangent to the curve at a specific point. Signup and view all the answers

How is concentration related to reaction rate?

Directly proportional Signup and view all the answers

Study Notes

Catalysts and Reaction Rates

Unstable intermediates form between a reactant and a catalyst, facilitating the reaction process.
Adsorption refers to the accumulation of one substance at the surface of another, crucial in catalytic processes.
Finely divided or porous catalysts significantly increase the reaction rate due to greater surface area for reactions.

Catalytic Poisons

Catalytic poisons block active sites on catalysts, reducing their effectiveness and lowering the reaction rate.
Tetraethyl lead is a common example of a catalytic poison.

Elements in Catalytic Converters

Platinum, palladium, and rhodium are the key elements that make up catalytic converters, essential for reducing automobile emissions.

Temperature and Reaction Dynamics

Increasing temperature results in an increased rate of reaction due to higher kinetic energy of particles.
There is an exponential relationship between temperature and reaction rate, indicating that small temperature increases can lead to large changes in rate.

Measuring Reaction Rates

The instantaneous rate of reaction is determined by drawing a tangent to the concentration vs. time curve at a specific point.
Concentration is directly proportional to the rate of reaction; higher concentrations lead to faster reaction rates.

Role of Catalysts

Catalysts provide active sites for reactions according to the surface adsorption theory without altering themselves chemically.
A catalyst is defined as a substance that alters the reaction rate but remains chemically unchanged at the end of a reaction.

Types of Catalysis

Heterogeneous catalysis occurs when the catalyst phase differs from the reactants, while homogeneous catalysis involves the catalyst being in the same phase.
Autocatalysis refers to reactions where one of the products acts as a catalyst, exemplified by the standardization of KMnO₄.

Activation Energy and Effective Collisions

Activation energy is the minimum energy required for colliding particles to react.
An effective collision requires sufficient activation energy and results in product formation.

Factors Affecting Reaction Rates

Increased concentration of reactants leads to an increased reaction rate.
The instantaneous rate of a reaction is defined as the change in concentration of a reactant or product per unit time at a specific point.
Manganese dioxide serves as a catalyst in the decomposition of hydrogen peroxide, enhancing the reaction rate.

Heat Change and Reaction Types

The sign of ΔH indicates the type of reaction: negative ΔH signifies an exothermic reaction (heat released), while positive ΔH indicates an endothermic reaction (heat absorbed).

Altering Activation Energy

The activation energy of a reaction can be reduced by adding a catalyst, providing an alternative pathway for the reaction.

Real-World Applications

Catalytic converters in cars exemplify the surface adsorption theory by transforming harmful pollutants into less harmful products.
The average rate of reaction can be calculated by dividing the total products produced by the total time.

Effects of Pressure

Increasing pressure boosts the reaction rate, applicable only to gaseous reactions.

Methods to Increase Reaction Rates

Options to enhance the reaction rate include increasing temperature, pressure (for gases), surface area, adding a catalyst, or raising reactant concentration.

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Description

Explore the role of catalysts in chemical reactions, including how unstable intermediates and adsorption facilitate processes. Learn about catalytic poisons that diminish catalyst effectiveness and the importance of key elements in catalytic converters. Additionally, understand the effect of temperature on reaction rates and dynamics.