chem 2 exam 1

Final energy of products is lower than reactants

reaction is exothermic, ΔHrxn = negative, releases heat

Final energy of products is greater than reactants

endothermic, Δrxn = positive, need heat to make reaction go

Activation energy

energy that must be overcome for reaction to proceed

always positive (if not gained by reaction, reaction can’t proceed)

catalysts lower activation energy (increases reaction rate without being consumed) (also speeds up forward and reverse reactions and doesn’t affect ΔH or overall yield for a reaction)

Transition state

enough energy is gained by reaction where old bonds are broken and new bonds form (converting reactants to products)

peak of hump → number of transition states (humps), number of steps in reaction

Activation energy is

not dependent on the temperature, but rate constant does depend on temperature

Arrhenius Equation

single rate: A * e^-Ea/RT

Equilibrium

state where forward and reverse reactions continue to occur at equal rates so no net change is observed once equilibrium is reached.

constant k

k

always greater than 0

if large (k>1) reaction is product favored, lies to the right

if small (k<1) reaction is reactant favored, lies to left

doesn’t tell us which way to shift - Q does (k is the number we’re trying to get to)

Reaction shifts

Q < k (reac → prod) shift right

Q = k (equili) no shift

Q > k (reac ← prod) shift left

Partial Pressure of A

P_A=X_A * P_Total

Kp and Kc

EQ→ 1. Balanced, 2. K’s match, 3. Same Temp

Δn= total moles of gas products - total moles of gas reactants

Le chatelier’s principle

1. change that disrupts EQ, 2. a shift that brings it back to EQ

temperature

exothermic ΔH in product (negative)

endothermic ΔH in reactant (positive)

• temp is only factor that changes actual value of k

• if you change temp and shift right, k increases

• if you change temp and shift left, k decreases

pressure

affects the side of reaction with most mols of gas (volume is opposite) (not same as partial pressure)

at equili, addition of a catalyst

has no effect on shift of the reaction

adding an inert gas (noble gas)

• at constant volume doesn’t affect equili (since pressures are allowed to change)

• at constant pressure, pressures of the components will decrease so it will shift EQ toward more moles of gas

endo

exo

• incr temp, incr k

• incr temp, decr k

arrhenius acid

arrhenius base

substance with H in formula that dissociates in water to yield H3O+

subatnce with OH in formula that dissociates in water to yield OH-

• reactions between acid and base are nuetralization reactions (produce H2O)

• strength of acid/base depends on how much H+ or OH- it releases into water (stronger they are, the more it dissociates and releases these)

strong electrolytes

strong acid, strong base, soluble salet - all dissociate completely in solution

weak electrolytes

weak acid, weak base, insoluble salt - do not dissociate completely in solution- more like 10%