2. Gases, Kinetics, and Chemical Equilibrium Flashcards
Activation Energy
KE of the coliding molecules must reach this threshold energy for products to occur.
Average Translational Kinetic Energy and the Temperature of a Gas
Keavg = (3/2)RT
Catalyst
Increases the rate of both FORWARD and REVERSE rxn by lowering Ea. It does not change the equilibrium conditions. It gets the rxn to equilibrium more quickly. It is not consumed and not altered.
Chemical Equilibrium
When the forward rxn rate equals the reverse rxn rate. There is no change in concentration of reactants or products. Point of greatest entropy.
Collision Model
the rate is proportional to the number of collisions of reactant molecules.
Dalton’s Law
Ptotal = P1 + P2 + P3_
Dalton’s Law Definition
Total pressure is the sum of the partial pressures.
Deviations from Ideal Gas Law (Volume and Pressure)
Volume of Gases (Vreal > Videal); Pressure of Gases (Preal < Pideal)
Diffusion
Spreading of one gas into another gas or into empty space.
Effusion
effusion rate1/effusion rate2 = squareroot (M2/M1)
Effusion Definition
Spreading of a gas from high pressure to very low pressure through a pinhole.
Equilibrium Constant K
When you set k of forward reaction equal to k of reverse reaction, get the Law of Mass Action equation.
Graham’s Law
v1/v2 = squaroot(m2/m1)
Graham’s Law Definition
Relationship of KE of two gases and their rms velocities.
Heterogeneous Catalyst
It is in a DIFFERENT phase than the reactants and products. Usually solids.
Homogeneous Catalyst
It is in the SAME phase as the reactants and products. Usually in gas or liquid phase.
Ideal Gas
These characteristics are not true for real gas. 1) Gas molecules have 0 volume. 2) Gas molecules exert no forces other than repulsive forces due to collisions. 3) Gas molecules make completely elastic collisions. 4) KE avg of gas molecules is directly proportional to the temperature of the gas.
Ideal Gas Law
PV = nRT (R = 0.08206 L atm K-1 mol-1, or 8.314 J K-1 mol-1)
Intermediates
Species that are products of one reaction and reactants of a later reaction in a rxn change.
Kinetic Molecular Theory
Model of an ideal gas, which lacks certain real gas characteristics.
Le Chatelier’s Principle
When a system at equilibrium is stressed, the system will shift in a direction that will reduce that stress.
Mean Free Path
Distance traveled by a gas molecule between collisions.
Order of Each Respective Reactant
1st order, 2nd order. Part of the rate law, determined experimentally.
Overall Order
When you add all the respective reactant together.
Partial Pressure
Pa = XaPtotal (X is the mole fraction of the gas. Mole fraction is moles of gas divided by total number of moles)
Partial Pressure Definition
The amount of pressure contributed by any gas in a gaseous mixture is called the partial pressure of that gas.
Rate Determining Step
The slowest elementary step determines the rate of the overall rxn. Elementary steps make up the reaction.
Rate Law
rate forward = kf[A]^a[B]^b (only an example!)
Rate Law Definition
Describes the progress of a rxn. Must be determined experimentally.
Reaction Quotient
Using the same equation as K, can predict the direction in which a rxn will proceed. Q = K (equilibrium). Q > K, moves left increases reactants. Q < K, moves right increases products.
Standard Molar Volume
22.4 L
Standard Temperature and Pressure (STP)
0C, 1atm
The Law of Mass Action
K = products^coef/reactants^coef
The Reaction Quotient
Q = products^coef/reactants^coef
Charles’ Law
volume of a gas is proportional to temperature at constant pressure.
Boyle’s Law
volume of a gas is inversely proportional to pressure at constant temperature.
Avogadro’s Law
volume of a gas is proportional to the number of moles at constant temp and pressure.
What are the two requirements for a reaction to produce products?
1) Enough energy, past activation energy. 2) proper orientation.
Rate of a reaction INCREASES/DECREASES with temperature?
INCREASES because more collisions with sufficient relative KE occur each second.
Zero Order Reaction
Plot [A] vs. t gives slope -k. The slope is CONSTANT, so the rate constant is constant.
First Order Reaction
Plot ln[A] vs. t gives slope -k. Has constant half life independent of [A].
Second Order Reaction
Plot 1/[A] vs. t gives slope k. Half life is dependent on [A]. Each consecutive half-life is twice as long as the last.
Third Order Reaction
Plot 1(2[A]^2) vs. t gives slope k.
Le Chatelier when increase pressure
Equilibrium shifts to the lesser moles.
