S_03 Flashcards
(38 cards)
Define Chemical Kinetics
Study of the rate (how fast) at which a chemical reaction occurs
Chemical Kinetics formulas reactants n products
Rate = - (Δ[reactants]) / Δt
Rate = (Δ[products]) / Δt
What happens to the average KE of particles and the temperature after an exothermic reaction?
since rxn is exothermic, the average energy of particles will increase. (Energy released by the reaction makes particles move faster)
Presence of a catalyst = ? (2)
more reactants particles will collide with an E>Ea
Faster reaction
Catalyst is not consumed in a reaction
Catalyst is not consumed in a reaction
Differential rate law
Rate = ∆C / ∆t
Average rate law
Average rate law = -∆[ ~] / ∆t
Instantaneous rate
Instantaneous rate = -d[~] / dt
Initial rate:
Initial rate: Instantaneous rate at t = 0
Comment on the reaction rate as reaction progresses.
As reaction progresses the rate of reaction decreases
[reactants] decreases = (2)
less collisions
Forward rate decreases
[products] increases = (2)
More collisions
Reverse rate increases
N2(g) + 3 H2(g) → 2 NH3(g) If [NH3] increases at a rate of 0.024 mol/L.s at a particular instant, calculate the rate of disappearance of H2 and the rate of Reaction
0.012 mol /L x s
Page 13
For the reaction: 2H2(g) + O2(g) → 2 H2O (g)
(a) Express the rate in terms of changes in [H2], [O2], and [H2O] with time.
(b) When [O2] is decreasing at 0.23 mol/L⋅s, at what rate [H2O] is increasing?
Page 14
Experimental Rate Laws
Rate = k[A]^x[B]^y
NH4+(aq) + NO21-(aq) → N2(g) + 2 H2Ol(l)
Reaction order?
First order in NH4+ (exponent of [ NH4+ ] = 1) First order in NO21- (exponent of [ NO2^1- ] = 1)
Second order overall (1 + 1 = 2 )
What is the rate law for the following reaction ? (Also calculate k + its units)
H2O(g) + CH3Cl(g) → CH3OH(g) + HCl(g)
PAGE 20
First-order reaction (first-order rate law):
- (∆[A]) / ∆t = k[A]
Integrated rate law for first order reaction
ln [A] small t = ln [A] small 0 - kt
Reaction half-life ( t1/2 ): (For first-order reaction)
⇒
[A] 1/2
[A] =
0
t Reaction half-life ( t1/2 ): (For first-order rea
1/2
2
Reaction half-life ( t1/2 ): (For first-order reactions)
at t=t(1/2) —-> [A] small (t1/2) = [A0] /2
The rate constant (k) for the thermal decomposition of N2O5
(First-order reaction: 2 N2O5(g) → 2 N2O4(g) + O2(g) ) at a particular temperature
is 7.8 x 10-3 s-1. What is the half-life of N2O5 at that temperature?
89s p.25
The decomposition of azomethane is a first-order reaction:
CH3-N=N-CH3(g) → N2(g) + C2H6(g). The pressure of azomethane has been
measured at two different intervals : at t = 1.00 x 102 s, Pazomethane = 2.20 x 102 torr;
and at t = 3.00 x 102 s, Pazomethane = 132 torr. Determine the rate constant at this
temperature.
K = 1.55 x 10^3 p.25
Second-order reaction: Rate law
1/ [A]t = 1/ [A]0 +kt
