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Chapter 18 Reaction Rates and Equilibrium
Key Concepts and Vocabulary
39
Chemistry
11th Grade
05/19/2012

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