Chapter 18 Flashcards
How is the rate of chemical change expressed?
Amount of reactant changing per unit time
Rate
Measure of speed of any change that occurs within an interval of time
Collision theory
Atoms, ions, and molecules can react to form products when they collide, provided that the particles have enough kinetic energy and correct orientation
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 name for activated complex
What four factors influence the rate of a chemical reaction?
Temperature, concentration, particle size, use of a catalyst
Inhibitor
Substance that interferes with the action of a catalyst
Reversible reaction
Reaction in which the conversion of reactants to products and the conversion of products to reactants occur simultaneously
Chemical equilibrium
A state of balance in which the rates of the forward and reverse reactions are equal; no net change in the amount of reactants and products occurs in the chemical system
How do the amounts of reactants and products change in a chemical system at equilibrium?
No net change occurs in the actual amounts of components of the system
Equilibrium position
Relative concentrations of the reactants and products at equilibrium; indicates whether the reactants or products are favored in the reversible reaction
Le Châtelier’s principle
If a stress is applied to a system in dynamic equilibrium, the system changes in a way the relieves the stress
What three stresses can cause a change in the equilibrium position of a chemical system?
Changes in the concentration of reactants or products, changes in temperature, and changes in pressure
Equilibrium constant (Keq)
The ration 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 does the value of Keq indicate about the equilibrium position of a reaction?
A value of Keq greater than 1 means that products are favored over reactants; a value of Keq less than 1 means that reactants are favored over products
Free energy
The energy available to do work
Spontaneous reaction
Reaction that favors the formation of products at specified conditions
What are two characteristics of spontaneous reactions?
Produce substantial amounts of products at equilibrium and release free energy
Nonspontaneous reaction
Reaction that does not favor the formation of products at the specified conditions
Entropy
Measure of the disorder of a system
Law of disorder
The natural tendency is for systems to move in the direction of maximum disorder or randomness
What part does entropy play in chemical reactions
An increase in entropy favors the spontaneous chemical reaction; decrease favors the nonspontaneous reaction
What two factors determine the spontaneity of a reaction?
The size and direction of enthalpy changes and entropy changes together determine whether a reaction is spontaneous
Gibbs free-energy change
The maximum amount of energy that can be coupled to another process to do useful work
Is the Gibbs free-energy change positive or negative in a spontaneous process?
Numerical value of G is negative in spontaneous processes because because the system loses free energy
