Chapter 18 Test Flashcards
rate
a measure of speed of any change that occurs within an interval of time
How is the rate of a chemical change expressed?
an amount of reactant changing per unit of time
collision theory
atoms, ions, and molecules can react to form products when they collide with one another, provided that the colliding particles have enough kinetic energy
activation energy
minimum energy that colliding particles must have in order to react
activated complex
unstable arrangement of atoms that forms momentarily at the peak of the activation-energy barrier
transition state
another term for activated complex
inhibitor
substance that interferes with the action of a catalyst
What are four factors that affect the rate of a chemical reaction?
temperature, concentration, particle size, and the use of catalyst
How do the amounts of reactants and products change in a chemical system at equilibrium?
no net change occurs in the actual amounts of the components of the system
What three stresses can cause a change in the equilibrium position of a chemical system?
changes in: concentration of reactants/products, temperature, and pressure
What does the value of Keq indicate about the equilibrium position of a reaction?
Keq >1: products are favored over reactants. Keq <1: reactants favored over products
reversible reaction
reaction in which the conversion of reactants to products and the conversion of products to reactants occur simultaneously
chemical equilibrium
state of balance in which the rates of the forward and reverse reactions are equal; no net change in the amounts of reactants and products occurs in the chemical system
equilibrium position
relative concentrations of the reactants and products at equilibrium
Le Châtelier’s Principle
If a stress is applied to a system in dynamic equilibrium, the system changes in a way that relieves the stress
equilibrium constant (Keq)
ratio of product concentrations to reactant concentrations at equilibrium, with each concentration raised to a power equal to the number of moles of that substance in the balanced chemical equation
What are two characteristics of spontaneous reactions?
produce substantial amounts of products at equilibrium; release free energy
What part does entropy play in chemical reactions?
increase in entropy favors spontaneous chemical reaction; decease favors nonspontaneous reaction
What two factors determine the spontaneity of a reaction?
the size and direction of enthalpy changes and entropy changes
Is the Gibbs free-energy change positive or negative in a spontaneous process?
negative in spontaneous processes because the system loses free energy
free energy
energy that is available to do work
spontaneous reaction
occurs naturally and favors the formation of products at specified conditions
nonspontaneous reaction
does not favor the formation of products at specified conditions; do not give substantial amounts of products at equilibrium
entropy (S)
measure of the disorder of a system
law of disorder
natural tendency of systems to move in the direction of maximum chaos or disorder
Gibbs free-energy change (ΔG)
maximum amount of energy that can be coupled to another process to do useful work
