Exam 2

Which of the following is (are) unaffected by reversing the direction in which a chemical equation is written?

A) The equilibrium concentrations

The average rate of a reaction is the rate of reaction at any given time.

A) True

If a reaction is exothermic, then the activation energy for the forward reaction is ____ the activation energy for the reverse reaction.

B) less than

Consider the following reaction: 4HCl (g) + O2 (g) <-> 2H2O (g) + 2Cl (g) with deltaH = -114.4 kJ One way to decrease the amount of chlorine present at equilibrium is

B) raising the temperature.

For which of the following reactions is Kc equal to Kp?

C) PCl3 (g) + 3NH3 (g) <-> 3 HCl (g) + P(NH2)3 (g)

At equilibrium

C) the forward and reverse rates are equal.

Strong acids:

HClO4 H2SO4 HI HBr HCl HNO3

Ionization Constants of Conjugate Acid-Base Pairs

KaKb = Kw

Comparing concentration and pressure

Kp = Kc (RT) ^n

In pure water or any aqueous solution the equilibrium constant of water is:

Kw = [H3O+] [OH-] = 1.00 x 10^-14

Strong bases:

OH-

Bases produce

OH- ions in water

average rate

[Br2] final - [Br2] initial/t final - t initial

percent ionization

[H+]/[HA]0 x 100%

Equilibrium

a state in which there are no observable changes as time goes by

Equilibrium constant (K)

a temperature dependent constant that represents the ratio of reactant and product concentration at equilibrium K = [products]^x/[reactants]^x

Effect of Concentration

an increase/decrease in concentration of any of the components of a reaction will shift the reaction to lower/raise that concentration

first order

as the reactant concentration doubles the rate doubles rate = k[A]^1

second order

as the reactant concentration doubles the rate quadruples rate = k[A]^2

Quadratic Equation

ax^2 + bx + c = 0

Bases can

be neutral or negatively charged

reaction quotient (Qc)

calculated by substituting the initial concentrations of the reactants and products into the equilibrium constant (Kc) expression

Rate of creation of product:

change in molarity of product/change in time

Strong acids and bases

completely dissociate

unimolecular reaction

elementary step with 1 molecule

bimolecular reaction

elementary step with 2 molecules

termolecular reaction

elementary step with 3 molecules

rate law

expresses the relationship of the rate of a reaction to the rate constant and the initial concentrations of the reactants raised to some power Rate = k[A]^x[B]^y Rate = reaction time k = rate constant [A] and [B] = concentration of reagents sum of all exponents (x + y) = reaction order

Effect of temperature

for endothermic or exothermic reactions heat can be written as a reactant or product, thus changing the temperature has the same impact as changing the concentration of any other reactant or product.

reaction mechanism

how do the atoms move during the reaction, are there multiple steps?

reaction rate

how fast does a chemical reaction occur?

Temperature dependence of the rate constant

k = A x e^(-Ea/RT)

Strong acids have

larger K values because they are product favored

Bronsed-Lowry bases

must have a lone pair of electrons to accept the H+

pH Scale Calculations:

pH = -log [H3O+] pOH = -log [OH-] [H3O+] = 10^-pH [OH-] = 10^-pOH Kw = 1.00 x 10^-14 pH + pOH = 14.00

Weak acids and bases

partially dissociate

Effect of Pressure and Volume

pressure changes only impact the system if one or more chemicals is in the gaseous form

instantaneous rate

rate for specific instance in time

zero order

reactant concentration does not effect the reaction rate rate = k[A]^0

When the concentration of A or B increased

shifts to products

When the concentration of C is continually decreased

shifts to products

When the concentration of C is decreased

shifts to products

When the concentration of A of B is decreased

shifts to reagents

When the concentration of C is increased

shifts to reagents

simple rate laws

show how the rate depends on the initial reactant(s) concentration(s)

rate-determining step

slowest step in the sequence of steps leading to product formation

intermediate

species that appear in a reaction mechanism but not in the overall balanced equation

Bases

substance that can accept the H+ ion from an acid; proton acceptors

catalyst

substance that increases the rate of a chemical reaction without itself being consumed; lower the activation energy

Acids

substances that can donate a H+ ion to another molecule or ion; proton donors

activation energy (Ea)

the minimum amount of energy required to initiate a chemical reaction

molecularity of a reaction

the number of molecules reacting in an elementary step

elementary steps/elementary reactions

the overall progress of a chemical reaction can be represented at the molecular level by a series

half life (t 1/2)

the time required for the concentration of a reactant to decrease to half of its initial concentration

integrated rate laws

used to determine the reactant concentration at any time

ICE Table

using the initial concentrations and the equilibrium constant to predict the concentrations at equilibrium

Le Chatelier's Principle

when a stress is applied to a system at equilibrium, the equilibrium shifts to relieve the stress. Stresses include changing concentration, pressure, temperature, or volume.

rate laws:

- are always determined experimentally - is always defined in terms of reactant concentrations - is not related to the stoichiometric coefficient of the reactant in the balanced chemical equation

Rate of consumption of reactant:

- change in molarity of reactant/change in time

Rate of chemical reaction depends on many factors:

- initial concentration of reagents - time - temperature - collision frequency - orientation - activation energy - reaction mechanism/multiple steps

Methods for increasing the reaction rate:

- reactant concentration - temperature - catalyst

Chemical equilibrium:

- the rates of the forward and reverse reactions are equal - the concentrations of the reactants and products remain constant

Adding a catalyst:

-does not change K -does not shift the position of an equilibrium system -system will reach equilibrium sooner -lowers Ea for both forward and revers reactions

Diprotic and Triprotic acids:

-lose one proton at a time -separate K expressions for each proton transfer -the Ka for removing the 2nd or 3rd protons is smaller than the previous Ka

Writing plausible reaction mechanisms:

-the sum of the elementary steps must give the overall balanced equation for the reaction -the rate-determining step should predict the same rate law that is determined experimentally