Rate & Rate Equations Flashcards
What is the definition/formula for rate?
Rate(moldm-3s-1) = Change in conc of reactants (moldm-3)/time (s-1)
Outline the relationship between rate and the concentration of reactants
Rate ∝ conc of reactants
or
Rate = k (rate constant) X conc of reactants
Outline the rate equation for 3A + 2B -> C + 2D
Rate = k[A]^m[B]^n
Define orders of the reaction and the overall order
Orders of Reaction = Power to which the conc of reactants are raised in the rate equation
Overall Order = sum of reaction orders
Define 0 order
Change of conc of reactant has no effect on rate
Define 1st order
Rate ∝ to conc of reactant
Define 2nd order
Rate = (Conc of reactant)^2
Outline how 0 order would look on a:
1. rate/conc graph
2. conc/time graph
- Horizontal line (same rate as conc increases)
- Straight line going down to time (x axis) from conc (y axis) as time increases
Outline how 1st order would look on a:
1. rate/conc graph
2. conc/time graph
- Straight line through origin
- Curved line going down (rate high with steep m as highest N° of reactant particles - frequent collisions)
Outline how 2nd order would look on a:
1. rate/conc graph
2. conc/time graph
- Curved line going up
- Curved line going down
How do you find the rate from a conc/time graph when the line is curved?
- Draw a tangent
- Find the gradient = rate
- Do multiple times to see if they increase/decrease by the same amount
Outline how you find the rate equation from the mechansim?
- Find the rate determining step (slowest- makes the least product)
- Put the reactants into rate equation
Outline the Arrhenius Equation and the units
k = Ae^-Ea/RT
k = rate constant
A = Arrhenius Constant (pre-exponential factor)
e = exponential factor
Ea = Activation Energy (Jmol-1)
R = Gas constant (8.31 JK-1mol-1)
T = Temperature (K)
Outline the logged version of the Arrhenius Equation
lnk = lnA -eA/RT
Outline the logged version of the Arrhenius equation as the equation of a straight line
lnk = -Ea/RT +lnA <—> Y = mx + c
