Chemistry Chapter: Collision Theory and Reaction Rates

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Questions and Answers

What is the effect on an exothermic reaction if heat is added?

The reaction shifts to the reactants. (correct)

The reaction shifts to the products.

The amount of product increases.

The reaction becomes more favorable.

In an endothermic reaction, what happens when heat is removed?

Heat is produced to counteract the change. (correct)

The equilibrium position remains unchanged.

The reaction shifts to the products.

The amount of reactants increases. (correct)

What role do colorimetric reactions play in observing Le Châtelier's Principle?

They determine the pressure changes in a reaction.

They allow for visual analysis of equilibrium shifts. (correct)

They help identify the concentration of reactants.

They measure temperature changes directly.

When vaporization occurs only at the surface of a liquid, this process is known as:

Evaporation Signup and view all the answers

In an equilibrium reaction, if the concentration of products is increased, what is the immediate effect on the reaction?

The reaction shifts to the left. Signup and view all the answers

What happens to the equilibrium position of a reaction when the pressure is decreased?

It shifts toward the side with more moles of gas. Signup and view all the answers

When ice melts, which statement accurately describes the energy changes?

The process requires energy to break hydrogen bonds. Signup and view all the answers

In an exothermic reaction, if heat is removed, what is the expected change in the system?

The reaction shifts toward the reactants. Signup and view all the answers

Which principle predicts the effect of a change on chemical equilibrium?

Le Châtelier’s Principle Signup and view all the answers

What happens when the concentration of a reactant is increased at equilibrium?

More products are produced to consume the added reactant Signup and view all the answers

In a reaction with equal moles of gas on both sides, how does increasing pressure affect the equilibrium?

There is no shift in equilibrium Signup and view all the answers

What occurs when the pressure in a reaction system is decreased and there are fewer moles of gas on one side?

The reaction shifts towards the side with more gas molecules Signup and view all the answers

How does removing a product from a reaction at equilibrium affect the system?

It shifts to produce more products Signup and view all the answers

When heat is added to an endothermic reaction, how does equilibrium shift?

Towards the products Signup and view all the answers

Why does the equilibrium position shift when there is a change in concentration?

To restore balance and reestablish equilibrium Signup and view all the answers

What happens to a reaction at equilibrium when temperature is decreased in an exothermic reaction?

The equilibrium shifts to favor the products Signup and view all the answers

What does a positive ΔH indicate about a chemical reaction?

The reaction is endothermic and absorbs energy. Signup and view all the answers

In a reversible reaction at equilibrium, what happens to the rates of the forward and reverse reactions?

The rates of both reactions become equal. Signup and view all the answers

Which of the following scenarios best illustrates Le Châtelier's Principle?

Adding reactants to a reaction system at equilibrium causes the formation of more products. Signup and view all the answers

What does it mean when the expression for the equilibrium constant K is less than 1?

Reactants are favored at equilibrium. Signup and view all the answers

What happens to the equilibrium position if the concentration of a reactant is decreased?

The equilibrium shifts towards the reactants. Signup and view all the answers

Which statement is true regarding exothermic reactions?

Temperature decreases as product formation occurs. Signup and view all the answers

How does increasing the pressure affect a gas-phase equilibrium reaction?

It shifts the equilibrium towards the side with fewer gas molecules. Signup and view all the answers

What is indicated by the presence of a double arrow in a chemical reaction?

The reaction reaches equilibrium. Signup and view all the answers

Study Notes

Collision Theory

Collision theory explains reaction rates.
For a chemical reaction to occur, reacting atoms must collide:
- With sufficient energy
- With the proper orientation

Reaction Rates

The rate of reaction is how quickly reactants form products.
As a reaction proceeds, reactant concentration decreases and product concentration increases.

Activation Energy

Activation energy is the minimum energy required for reacting particles to collide and react.
Activation energy is like the 'hill' reactants must overcome before products form.

Factors Affecting Reaction Rates - Chemical Nature of Reactants

Reactants must have compatible chemistry to react.
Example: Noble gases do not react because they are already stable.

Factors Affecting Reaction Rates - Temperature

Increasing temperature increases particle speed and energy.
Faster-moving particles collide more frequently and with more energy, increasing reaction likelihood.

Factors Affecting Reaction Rates - Concentration

Concentration refers to the amount of solute dissolved in a solution.
Increasing reactant concentration increases the number of particles, leading to more frequent collisions, thus increasing reaction rates.

Factors Affecting Reaction Rates - Surface Area

Breaking a solid into smaller pieces increases its surface area.
Increased surface area allows more collisions with reactant particles, increasing reaction rates.

Factors Affecting Reaction Rates - Catalysts

Catalysts provide an alternative reaction pathway with less activation energy.
Catalysts speed up the reaction without being consumed in the process.

Enthalpy

Enthalpy (H) is the chemical potential of a substance, measured in kilojoules (kJ).
Enthalpy change (ΔH) is the change in energy during a reaction.
ΔH = H(products) - H(reactants), measured in kilojoules per mole (kJ/mol).

Enthalpy Change of a Reaction

Positive ΔH indicates an endothermic reaction (absorbs energy).
Negative ΔH indicates an exothermic reaction (releases energy).

Potential Energy Diagram

A potential energy diagram shows energy changes during a chemical reaction.
ΔH is negative for exothermic reactions and positive for endothermic reactions.

Enthalpy Changes in Chemical Equations

Enthalpy change (ΔH) is written to the right of a chemical equation.
A positive ΔH value represents an endothermic reaction, and a negative value represents an exothermic one.

Chemical Equilibrium

In many chemical systems, reactions can proceed in both forward and reverse directions.
These are called reversible reactions.
A reaction reaches equilibrium when the forward and reverse reaction rates are equal.
The amounts of reactants and products at equilibrium are constant.

Le Chatelier's Principle

Le Chatelier's Principle predicts how a change in conditions affects a reaction at equilibrium.
A disturbance in the reaction will shift to counteract the change and restore equilibrium.
Three key disturbances to equilibrium are concentration, pressure, and temperature.

What Happens if Concentration Changes?

Adding reactant or product increases reactant / product concentration.
The reaction shifts away from the added substance to consume it.
Removing reactant or product decreases concentration.
The reaction shifts towards the removed substance to produce more of it.

What Happens if Pressure Changes?

Increasing pressure shifts the reaction toward the side with fewer gas molecules.
Decreasing pressure shifts the reaction toward the side with more gas molecules.

What Happens if Heat is Added or Removed?

In exothermic reactions, heat is a product.
Adding heat shifts the reaction towards the reactants.
Removing heat shifts the reaction towards the products.
In endothermic reactions, heat is a reactant.
Adding heat shifts the reaction towards the products.
Removing heat shifts the reaction towards the reactants.

Lab 5.5 Observing Le Chatelier's Principle

Some equilibrium reactions are colorimetric (where substances have different colors).
Color changes can be used to observe Le Chatelier's principle and analyze the direction of equilibrium shifts.

Phase Changes Requiring Energy

Melting: Ice gains energy, hydrogen bonds break, molecules move apart to form liquid.
Vaporization/Evaporation: Liquid molecules gain energy, forces of attraction break, liquid becomes a gas. This may occur at the surface only (evaporation).
Sublimation: Solid molecules gain energy, forces of attraction break, solid becomes a gas directly.

Phase Changes Releasing Energy

Condensation: Gas/vapor molecules lose energy, velocity decreases, hydrogen bonds form, gas/vapor becomes a liquid.
Freezing: Liquid molecules lose energy, molecules become fixed in place, liquid becomes a solid.
Deposition: Gas/vapor molecules lose energy, velocity decreases, molecules become fixed in place, gas/vapor becomes a solid.

Heating and Cooling Curves

A graph of temperature versus time for a substance.
Phase changes are represented by horizontal (plateau) lines.
Each substance has a different heating/cooling curve.

Phase Diagrams

A graph combines pressure and temperature to show phase changes of a substance.
The triple point is where all three phases (solid, liquid, and gas) coexist in equilibrium.
A critical point is where the liquid and gas phases become indistinguishable.

Heat Capacity and Specific Heat Capacity

Heat capacity is the amount of heat required to change the temperature of a substance by 1 °C.
Specific heat capacity is the amount of heat required to raise the temperature of one gram of a substance by 1 °C.

Calculating Specific Heat

Specific heat (c) is calculated using the formula q=mcΔTq=mc\Delta Tq=mcΔT.

Activity 5.8A Investigating Specific Heat Capacity

The material requiring the most heat energy to show a small temperature change has the highest specific heat capacity.
Water has the highest specific heat capacity.

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Description

This quiz covers the fundamental concepts of collision theory, reaction rates, and activation energy in chemistry. Explore how the nature of reactants, temperature, and other factors influence the rate of chemical reactions. Test your knowledge on the essential principles that govern these chemical processes.