GC2 Exam I

Collision theory

a reaction occurs only when the species reacting collide with enough energy to overcome the activation energy and in a perfect orientation

things that increase reaction rates (collision theory)

1. increasing the # of collisions

2. increasing the temperature

3. increasing the reactants concentration

how to use rearranged rate laws

1. collect concentration

2. plot concentration

3. linear plot = reaction order

• consentration vs. time = zero order

• natural log = first order

• 1/concentration = second order

exothermic reaction coordinate diagram

a diagram where the reactants start at a higher energy level than the products

endothermic reaction coordinate diagram

a diagram where the reactants start at a lower energy level than the products

high activation energy indicates …

a slow reaction

low activation energy indicates …

a fast reaction

when temp and reaction rate increase …

activation energy stays the same

how to graphically solve for activation energy

1. plot points

• X-axis = 1/T

• Y-axis = lnk

1. determine the slope

2. set slope equal to Ea/R

unimolecular step

an elementary step that involves 1 species

bimolecular

an elementary step that involves 2 species

termolecular

an elementary step that involves 3 species

intermediate

a species that is formed in one step and then consumed in a later step (removed from net)

reversible elementary steps

steps that can proceed in the forward and the reverse direction

rate law rules for reversible steps

1. the rate law is the slowest reversible step

2. if an intermediate is in the rate law set k1=k_1

• rate law will usually = reactants in fast step

chemical equilibrum

a state where the rate of the forward reaction is equal to the rate of the reverse reaction (rates are equal but rate laws dont need to be)

product favored reaction

a reaction that occurs when the concentration of products is greater than the concentration of reactants at equilibrium

product favored reaction criteria

1. K > 1

2. K_forward > K_reverse

3. system contains mostly products

reactant favored reaction

a reaction that occurs when the concentration of reactants is greater than the concentration of products at equilibrium

reaction favored reaction criteria

1. K < 1

2. K_reverse > K_forward

3. system contains mostly reactants

2 things that wont appear in an expression

1. pure solids

2. pure liquids/solvents

3 ways to manipulate equilibrium constant expressions

1. multiplying the equation by a constant (n)

2. writing the reaction in a reverse direction

3. combining the equation with another equation

what is K_new when the equation is multiplied by n?

K_new = (K_old)^n

what is K_new when the equation is reversed?

K_new = 1/K_old

what is K_new when the equation is combined?

K_new = K_1 X K_2

ICE method rules

1. reactants = -x

2. products = +x

Q < K

1. reactants decrease

2. products increase

3. system shifts right

Q > K

1. reactants increase

2. products decrease

3. system shifts left

2 changes that causes a right shift

1. increase in reactants

2. decrease in products

2 changes that causes a left shift

1. decrease in reactants

2. increase in products

a change in the systems volume only impacts…

gas-phase equilibria

how does the system shift when volume decreases?

the system shifts in the direction that produces fewer moles of gas

how does the system shift when volume decreases?

the system shifts in the direction that produces more moles of gas

when the temp increases during an exothermic reaction…

1. system shift lefts

2. K decreases

when the temp decreases during an exothermic reaction…

1. system shifts right

2. K increases

when the temp increases during an endothermic reaction…

1. system shifts right

2. K increases

when the temp decreases during an endothermic reaction…

1. system shifts left

2. K decreases