Questions and Answers
Which of the following describes the effects of change in concentration on a chemical system in equilibrium?
Le Châtelier's principle
Changes in which of the following do not shift the equilibrium of a chemical system?
Time
What happens in a reaction if it is at chemical equilibrium?
The rate of the forward reaction equals the rate of the reverse reaction.
Which of the following represents an increase in entropy?
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What is a negative Gibbs free-energy value an indication of?
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What happens to a catalyst as the result of a chemical reaction?
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What is the equilibrium for 2NO + Br2 --> 2NOBr?
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Consider the reaction 2NaN3 -> 2Na + 3N2, which is the first reaction that occurs when an air bag expands in a car undergoing a collision. What does the graph showing the amount of nitrogen gas (N2) look like?
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A chemical reaction is at equilibrium. What will be the effect if more of the product is added?
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Which of the following is likely to occur if more reactants are added to a reaction that is at chemical equilibrium?
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What can you calculate if you know the concentration of a reaction's products and reactants, as well as the coefficients of each in the balanced equation?
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What does the formula ΔH - TΔS determine?
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What is the equation for the equilibrium constant for the equation CO + 3H2 --> CH4 + H2O?
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Which of the following equations is used to describe reaction rates?
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Molecules involved in a chemical reaction must collide to react. What is this concept called?
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What kind of reaction occurs when the entropy change of an endothermic reaction is negative?
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What type of reaction will occur if ΔH is negative and there are no significant entropy effects?
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Which of the following factors does not increase the rate of a reaction?
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What term refers to the difference between the energy of the transition state and the energy of the reactants?
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Adding an inhibitor to a chemical reaction will have which of the following effects on the reaction?
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Study Notes
Equilibrium Principles
- Le Châtelier's principle explains how changes in concentration affect a chemical system in equilibrium.
- Adding more products shifts the equilibrium to the left, toward reactants.
- Adding more reactants shifts the equilibrium to the right, toward products.
Reaction Dynamics
- A chemical reaction at equilibrium occurs when the rate of the forward reaction equals the rate of the reverse reaction.
- A catalyst remains unchanged after a reaction and is not consumed.
Entropy and Gibbs Free Energy
- The diffusion of green food coloring through cookie dough represents an increase in entropy.
- A negative Gibbs free energy value indicates a spontaneous reaction.
- The formula for Gibbs free energy is ΔH - TΔS, where ΔH is the change in enthalpy and ΔS is the change in entropy.
Reaction Rates and Constants
- The equilibrium constant for the reaction 2NO + Br2 ⇌ 2NOBr is expressed as [NOBr]²/[NO]²[Br2].
- The equation for reaction rates is Δ[reactant or product]/Δtime.
- Knowledge of concentrations and coefficients allows calculation of the equilibrium constant.
Collision Theory
- Collision theory states that molecules must collide with sufficient energy to react.
- Decreasing the temperature of a system does not increase reaction rates; in fact, it generally lowers them.
Endothermic and Spontaneous Reactions
- Nonspontaneous reactions at equilibrium occur when the entropy change of an endothermic reaction is negative.
- Spontaneous reactions are expected if ΔH is negative and entropy effects are not significant.
Inhibitors
- Inhibitors decrease the rate of chemical reactions.
Activation Energy
- The difference in energy between the transition state and the energy of the reactants is known as activation energy.
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