Chapter 12 Key Terms

activated complex/transition state

unstable combination of reactant species formed during a chemical reaction

activation energy

minimum energy needed in order for a reaction to take place

arrhenius equation

mathematical relationship between a reactions rate constant, activation energy, and temperature

average rate

rate of a chemical reaction computed as the ratio of a measured change in amount of concentration of substance to the time interval over which the changes occured

bimolecular reaction

elementary reaction involving two reactant energies

catalyst

substance that increases the rate of a reaction without itself being consumed by the reaction

collision theory

model that emphasizes the energy and orientatino of molecular collisions to explain and predict reaction kinetics

elementary reaction

reaction that takes place in a single step; precisely as depicted in its chemical equation

frequency factor

proportionality constant in the arrhenius equation, related to the relative number of collisions having an oreintation capable of leading to product formation

half life

time required for half of a given amount of reactant to be consumed

heterogenous catalyst

catalyst present in a differente phase from the reactants, furnishing a surface at which a reaction can occurh

homogenous catalyst

catalyst present in the same phase as the reactants

initial rate

instantaneous rate of chemical reaction at t=0, right after the reaction has begun

instantaneous rate

rate of chemical reaction at any instant time; determined by slope of the line tangential to a graph of concentration as a function of time

integrated rate law

equation that relates the concentration of a reactant to elapsed time of a reaction

intermediate

entities produced in one step of a reaction mechanism and consumed in a subsequent step

method of initial rates

common experimental approach to determining the rate laws that involves measuring reaction rates at varying initial reactant concentration

molecularity

number of reactant entities involved in an elementary reaction

overall reaction order

sum of reaction orders for each substance represented in the rate law

rate constant (k)

proportionality constant in a rate law

rate expression

mathematical representation defining reaction rate as a change in amount, concentration, or pressure of reactant or product species per unit time

rate law

mathematical equation showing the dependence of reaction rate on the rate constant and the concentration of one or more reactants

rate of reaction

measure of the speed at which a chemical reaction takes place

rate determining step

slowest elementary reaction in a reaction mechanism; determines rate of overall reaction

reaction mechanism

stepwise sequence of elementary reactions by which a chemical change takes place

reaction order

value of an exponent in rate law

termolecular reaction

elementary reaction involving three reactant entities

unimolecular reaction

elementary reaction involving a single reactant entitiy

why can warm lizards move faster than cold lizards

the chemical reactions that allow muscles to move occur more rapidly at higher temperatures

in a car slowing down, what is the initial rate

the speedometer reading at the instant the brake pedal is pressed

in a slowing down car, what is the instantaneous rate

the speedometer reading during braking process

in a slowing down car, what is the average rate

the ratio of distance travelled in the time it took to slow the car to a complete stop

factors affecting reaction rates

1. the chemical nature of reacting substances

2. physical states of the reactants

3. temperature of the reactants

4. concentration of the reactants

5. the prescence of a catalyst

why is the reaction rate higher in smaller particles than larger particles

the surface area in contact with other reactant phase is greater

true or false

reaction rates are higher in colder temperatures

false

true or false

reaction rate increases when the concentration of reactants increases

true

what causes increased weathering in limestone and marble statues

pollutants

what is collision theory based on

1. the rate of reaction is proportional to the rate of reactant collisions

2. the reacting species must collide in an orientation that allows contact between the atoms that will become bonded together in the product

3. the collision must occur with adequate energy to permit mutual penetratin of the reacting species’ valence shells so that the electrons can rearrange and form new bonds