Chapter 18 Reaction Rates and Equilibrium – Flashcards
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| How is the rate of a chemical change expressed? |
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| in chemistry, the rate of chemical change or the reaction rate is usually expressed as the amount of reactant changing per unit time. |
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| What four factors influence the rate of a chemical reaction? |
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| the rate of a chemical reaction depends upon temperature, concentration, particle size, and the use of a catalyst. |
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| Rate |
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| a measure of the speed of any change that occurs within an interval of time. |
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| Collision theory |
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| atoms, ions, and molecules can react to form products when they collide with one another, provided that the colliding particles have enough kinetic energy. |
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| Activation energy |
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| the minimum energy that colliding particles must have in order to react. |
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| Activated complex |
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| an unstable arrangement of atoms that forms momentarily at the peak of the activation-energy barrier. |
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| Transition state |
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| another name for the activated complex |
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| Inhibitor |
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| a substance that interferes with the action of a catalyst. |
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| How do the amounts of reactants and products change in a chemical system at equilibrium? |
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| At chemical equilibrium, no net change occurs in the actual amounts of the components of the system. |
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| What three stresses can cause a change in the equilibrium position of a chemical system? |
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| stresses that upset the equilibrium of a chemical system include changes in the concentration of reactants of products, changes in temperature, and changes in pressure. |
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| What does the value of Keq indicate about the equilibrium position of a reaction? |
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| a value of Keq greater than 1 means that products are favored over reactants; a vlaue of Keq less than 1 means that reactants are favored over products. |
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| Reversible reaction |
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| one in which the conversion of reactants to products and the conversion of products to reactants occur simultaneously. |
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| Chemical equilibrium |
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| the rates of the forward or reverse reactions are equal, the reaction has reached a state of balance. |
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| Equilibrium position |
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| indicates whether the reactants or products are favored in a reversible reaction. |
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| Le Chatelier's principle |
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| if a stress is applied to a system in dynamic equilibrium, the system changes in ways that relieves the stress. |
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| Equilibrium constant (Keq) |
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| the ratio of product concentrations to reactant concentrations at equilibrium, with each concentratiion raised to a power equal to the number of moles of that substance in the balanced chemical equation. |
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| What is the relationship between the solubility product constant and the solubility of a compound? |
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| the smaller the numerical value of the solubility product constant, the lower the solubility of the compound. |
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| How can you predict whether precipitation will occur when two salt solutions are mixed? |
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| if the product of the concentrations of two ions in the mixture is greater than the Ksp of the compound formed from the ions, a precipitation will form. |
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| Solubility product constant (Ksp) |
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| equals the product of the concentrations of the ions each raised to a power equal to the coefficient of the ion in the dissociation equation. |
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| Common ion |
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| an ion that is found in both salts in a solution. |
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| Common ion effect |
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| the lowering of the solubility of an ionic compound as a result of the addition of a common ion. |
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| What are two characteristics of spontaneous reactions? |
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| spontaneous reactions produce substantial amounts of products at equlibrium and release free energy. |
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| What part does entropy play in chemical reactions? |
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| an increase in entropy favors the spontaneous chemical reation; a decrease favors the nonspontaneoud reaction. |
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| What two factors determine the spontaneity of a reaction? |
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| the size and direction of enthalpy changes and entropy changes together determine whether a reaction is spontaneous; that is, whether it favors products and releases free energy. |
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| Is the Gibbs free-energy change positive or negative in a spontaneous process? |
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| the numerical value of delta G is negative in a spontaneous process because the system loses free energy. |
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| Free energy |
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| energy that is available to do work. |
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| Spontaneous reaction |
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| occurs naturally and favors the formation of products at the specified conditions. |
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| Nonspontaneous reaction |
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| a reaction that does not favor the formation of products at the specified conditions. |
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| Entropy (delta S) |
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| a measure of the disorder of a system. |
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| Law of disorder |
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| states that the natural tendency is for a system to move in the direction of maximum disorder or randomness. |
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| Gibbs free-energy change |
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| the maximum amount of energy that can be coupled to another process to do useful work. |
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| What is the general relationship between the value of the specific rate constant,k, and the speed of a chemical reaction? |
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| the value of the specific rate constant,k, is large if the products form quickly; the value is small if the products form slowly. |
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| What do the hills and valleys in a reaction progress curve represent? |
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| the peaks correspond to the energies of the activated complexes. Each valley corresponds to the energy of an intermediate. |
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| Rate law |
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| an expression for the rate of a reaction in terms of the concentration of reactants. |
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| Specific rate constant (k) |
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| a proportionality constant relating the concentrations of reactants to the rate of the reaction. |
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| First-order reaction |
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| the reaction rate is directly proportional to the concentration of only one reactant. |
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| Elementary reaction |
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| a reaction in which reactants are converted to products in a single step. |
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| Reaction mechanism |
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| the series of elementary reactions or steps that take place during the course of a complex reaction. |
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| Intermediate |
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| a product of one of the steps in the reaction mechanism. |
