Rate and Equilibrium Flashcards
Definition of rate constant
The constant that links the rate of reaction with the concentrations of the reactants raised to the power of the orders in the rate equation
Definition of rate of reaction
The change in concentration of a reactant or product per unit time
Definition of half-life
The time taken for the concentration of the reactant to reduce by half
Definition of rate-determining step
The slowest step in the reaction mechanism of a multi-step reaction
The half life of a first-order reaction is…
Independent of the concentration
Formula of the rate equation
rate=k[A]^m[B]^n
What is the effect of temperature change on a rate constant?
-raising the temperature speeds up the rate of most reactions by increasing the constant, k.
Expression for Kc
Kc=[products]/[reactants]
What is the effect of increasing temperature on the value of Kc for exothermic reactions?
Shifts to the left (endothermic direction)
What is the effect of increasing temperature on the value of Kc for endothermic reactions?
Shifts position to the right (endothermic direction)
What is the effect of decreasing temperature on the value of Kc for exothermic reactions?
Shifts to the right (exothermic direction)
What is the effect of decreasing temperature on the value of Kc for endothermic reactions?
Shifts to the left (exothermic direction)
What is Kc unaffected by?
Concentration, pressure and catalysts
What is Kc affected by?
Changes in temperature
Zero-order concentration-time graph
- Concentration decreases at a constant rate.
- half-life decreases with time
First order concentration-time graph
- Concentration halves in equal time intervals.
- half-life is constant
Second order concentration-time graph
- concentration decreases rapidly, but the rate of decrease then slows down.
- half-life increases with time
Zero order rate-concentration graphs
- Rate is proportional to [A]^0
- The rate is unaffected by changes in concentration.
- As x increases, y stays constant
First order rate-concentration graphs
The rate is proportional to [A]^1
-If conc increases by 2 times, the rate does as well.
Second order rate-concentration graphs
rate is proportional to [A]^2
- if A increases by 2 times, rate increases by 4
- if A increases by 3 times, the rate increases by 9 times.
How to calculate pH from strong acids
pH=-log[acid]
because strong acids fully dissociate so [H+]=[acid]
How to calculate pH of weak acids
Use Ka:
-For weak acids, [H+]=[A-] because the acid dissociates to the both ions equally
- Ka=([H+]^2)/[HA]
pH= -log(root(Ka x [HA]))
How do we calculate Ka for weak acids?
Ka= [H+][A-]/[HA]
Ka=[H+]^2/[HA]
Calculate the pH of strong bases using Kw
Kw=[H+][OH-]=1.00 x10^-14
Gives you pOH or pH
pH=14-pOH
