Chapter 9 - Rate Processes Flashcards
Define the equation for rate of reaction
rate = k [A]^m [B]^n
where m is the order of reaction for A and n is the order of reaction for B. The overall order is m + n
K is a constant but will increase with an increase in temp
Define 0 order, 1st order and 2nd order
0 order is [A]t = -kt + [A]o downward slope not meeting the x axis
1st order is ln[A]t = -kt + ln[A]o downward slope meeting x axis
2nd order is 1/[A]t = kt + 1/[A]o upward slope starting above zero on y axis
What is the rate-determining step
The slowest stop with the greatest peak on a graph is the rate-determining step
Define the rate constant k
K = Ae^-Ea/RT
where A is arrhenius constant (frequency and orientation of collision)
E is the activation energy
R is the gas constant and T is the absolute temperature
What is the relationship between Gibbs and stability
The lower the Gibbs, the more stable
Affect of temperature on the rate constant
Rate constant is only constant where temperature is constant
in increase in temp = increase K = decrease in activation energy
What does an exothermic and endothermic graph look like
EXO = heat out, is -ve so end of curve lower than start of curve ENDO = head used, is +ve so end of curve higher than start of curve
What is an activated complex
Activated complex is from start of curve to peak of curve so smaller activation complex in EXO (since start of curve is higher than endo).
Smaller activation complex (EXO) = faster
Bigger difference in activation complex (ENDO) = slower
Difference between thermodynamically controlled and kinetically controlled
Reactants that form a product that requires smallest amount of energy is THERMODYNAMICALLY controlled
Reactants that form a product with the lowest gibbs free energy meaning is the most stable is KINETICALLY controlled
What does a catalyst do with respect to activation energy
Catalysts provide an alternate mechanism of different transition state with a LOWER activation energy making the rate increase. Catalysts don’t participate in the reaction, they stabilise transition states.
Catalysts are big molecules with at least one active site, catalysts don’t alter the equilibrium because they don’t change the energy difference between the reactants and products. Catalysts make a smaller peak on a graph
5 moles of X and 12 moles of Y yield 4 moles of Z in a 1L container. What is K
If 4 moles result, then 4X and 8Y are used (molar ratios) so 1X and 4Y remain so equilibrium concentrations are 1mol X and 4mol Y and Z
K = [Z]/[X][Y]^2 = 4/1x4^2 = 0.25
What is the role of K in determining forward and reverse favourability
K>1 forward reaction favoured
K<1 reverse reaction favoured (so won’t proceed and little product is formed)
K=1 neither forward or reverse is favoured
*pure solids and liquids don’t appear in Keq as their concentrations remain the same
Define equation for △G
△G = △H - T△S △G = -RT ln Keq
What can change the equilibrium constant?
Temperature can change Eq
Concentration, volume and pressure can shift position but can’t change the value itself
