Class notes B.sc-007

Question:
1. A reaction has a rate constant of 0.0113 s−1s−1 at 400.0 KK and 0.684 s−1s−1 at
450.0 K.
Determine the activation barrier for the reaction.
Express your answer in kilojoules per mole to three significant figures.

2. Ethyl chloride vapor decomposes by the first-order reaction
C2H5Cl→C2H4+HClC2H5Cl→C2H4+HCl
The activation energy is 249 kJ/mol and the frequency factor is 1.6×1014s−11.6×1014s−1.

Find the fraction of the ethyl chloride that decomposes in 10 minutes at this temperature.
Express your answer using one significant figure.

3. Consider this three-step mechanism for a reaction:
Cl2(g)Cl(g)+CHCl3(g)Cl(g)+CCl3(g)⇌k1k2−→k3−→k42Cl(g)HCl(g)+CCl3(g)CCl4(g)(fast)(sl
ow)(fast)

What is the overall reaction?
Express your answer as a chemical equation. Identify all of the phases in your
answer.

4. Consider the reaction
8H2S(g)+4O2(g)→8H2O(g)+S8(g)8H2S(g)+4O2(g)→8H2O(g)+S8(g)
Δ[H2S]/ΔtΔ[H2S]/Δt = -0.040 M/s

a. Find Δ[O2]/ΔtΔ[O2]/Δt.
Express your answer to two significant figures and include the appropriate units.
Include the sign only if the value is negative.

b. Find Δ[H2O]/ΔtΔ[H2O]/Δt.
Express your answer to two significant figures and include the appropriate units.
Include the sign only if the value is negative.

c. Find Δ[S8]/ΔtΔ[S8]/Δt.
Express your answer to two significant figures and include the appropriate units.
Include the sign only if the value is negative.

d. Find the rate of the reaction.
Express your answer to two significant figures and include the appropriate units.


Ans 1) Activation energy barrier =123.1 KJ/mol



Ans 2) The fraction of the reactant molarity decomposed is:=0.035

, Ans 3) Add up the 3 steps:



Cl2(g) + Cl(g) + CHCl3(g) + Cl(g) + CCl3(g) => 2 Cl(g) + HCl(g) + CCl3(g) + CCl4(g)



Cancel common terms to get overall reaction:



Cl2(g) + CHCl3(g) => HCl(g) + CCl4(g)



Ans 4 )



a)0.02



b)-0.04



c) 0.005



d) 0.005