CHEMISTRY 12 – COLLISION THEORY & ENERGY CHANGES WORKSHEET
1) Using collision theory, give two reasons why reactions occur more rapidly at a higher temperature.
(2 marks)
There is a greater fraction of collisions with sufficient energy.
There are more frequent collisions because the particles are moving faster.
2) A reaction does not always occur when two reactant particles collide. Give two reasons why.
(2 marks)
A reaction does not occur if there is insufficient energy.
A reaction does not occur if there is incorrect orientation (geometry).
3) Consider the following reaction:
Mg (s) + 2 HBr (aq) → MgBr2 (aq) + H2 (g) + energy
In terms of collision theory, describe how each of the factors below would influence the reaction
rate. (3 marks)
a) Increasing the concentration of HBr
Increasing the concentration of HBr will increase the # of particles, therefore increase the # of
collisions, therefore increase the reaction rate.
b) Decreasing the temperature
Decreasing the temperature will decrease the speed of the particles and decrease the average KE
of the particles, therefore there will be fewer collisions with sufficient energy to overcome the
repulsive forces therefore decrease the reaction rate.
c) Increasing the surface area of Mg
Increasing the surface area of Mg will increase the # of particles that are exposed and available to
react, therefore increase the # of collisions and therefore increase the reaction rate.
4) Consider the following KE distribution curve for colliding particles:
a) Sketch a line on the graph to the left, for the
distribution of collisions at a higher
temperature. (2 marks)
b) Shade in the area representing the collisions
that could result in forming an activated
complex at the lower temperature. (1 mark)
5) Consider the following reaction:
C (s) + O2 (g) → CO2 (g) + 394 kJ
In terms of collision theory, describe how each of the factors below would influence the reaction
rate. (3 marks)
a) Decreasing the concentration of O2
Decreasing the concentration of O2 will decrease the # of particles, therefore decrease the # of
collisions, therefore decrease the reaction rate.
b) Increasing the temperature
Increasing the temperature will increase the speed of the particles and increase the average KE of
the particles, therefore increase the # of successful collisions which will increase the reaction
rate.
c) Decreasing the surface area of C
Decreasing the surface area of C will decrease the # of particles exposed and available for
collisions, therefore will decrease the # of collisions and therefore decrease the reaction rate.
6) Consider the following reaction occurring in a 1.0 L container:
H2 (g) + I2 (g) → 2 HI (g)
State two requirements for a successful collision between H2 and I2. (2 marks)
Favourable collision geometry/orientation and sufficient KE are required for a successful collision.
7) Which of the following reactions would have a negative value for ΔH (there are more than one
answers) (1 mark)
I.
The evaporation of water
III. The explosive reaction between H2 and O2
II.
The burning of a match
IV. A chemical cold pack
8) Rewrite the following reactions including the energy term. (4 marks)
a) 2 NO (g) + O2 (g) → 2 NO2 (g)
ΔH = +112 kJ
2 NO (g) + O2 (g) + 112 kJ → 2 NO2 (g)
b) C (s) + O2 (g) → CO2 (g)
ΔH = -394 kJ
C (s) + O2 (g) → CO2 (g) + 394 kJ
c) CaO (s) + 3 C (s) → CaC2 (s) + CO (g)
ΔH = +464.8 kJ
CaO (s) + 3 C (s) + 464.8 kJ → CaC2 (s) + CO (g)
d) CaO (s) + H2O (l) → Ca(OH)2 (aq)
ΔH = -65.2 kJ
CaO (s) + H2O (l) → Ca(OH)2 (aq) + 65.2 kJ
9) Determine the ΔH for the following reactions and state whether the reaction is endothermic or
exothermic. (2 marks)
a) CH4 (g) + 2 O2 (g) → CO2 (g) + 2 H2O (l) + 890.3 kJ
ΔH = - 890.3 kJ
exothermic
b) 2 Na2O2 (s) + 2 H2O (l) + 287.0 kJ → 4 NaOH (aq) + O2 (g)
ΔH = + 287.0 kJ
endothermic
c) 2 H2 (g) + O2 (g) → 2 H2O (l) + 572 kJ
ΔH = - 572 kJ
exothermic
d) 28 kJ + H2 (g) + I2 (g) → 2 HI (g)
ΔH = + 28 kJ
endothermic
10) When carbon monoxide and nitrogen dioxide react, 234 kJ is released. Which of the following
correctly represent this reaction?
I & IV
11) Consider the decomposition of ammonia:
2 NH3 (g) → N2 (g) + 3 H2 (g)
When 1.0 mol NH3 reacts, 46 kJ of energy is absorbed. Rewrite the equation for this reaction,
including the value of the heat term. (1 mark)
2 NH3 + 92 kJ → N2 + 3 H2
12) Draw a graph of “enthalpy” versus “reaction proceeds”, showing the relative enthalpies of the
reactant(s) and products(s), and the enthalpy changes, for the following reactions. (2 marks)
a) H2 (g) + S (s) → H2S (g) + 20 kJ
b) N2O4 (g) + 59 kJ → 2 NO2 (g)
2
enthalpy
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enthalpy
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