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Chem Test 3
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Exam of 4 pages for the course Chem1050 at U of G (Chem test)
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NUCLEUS HIGH SCHOOLUnit Test Unit - Rates of Reaction
KNOWLEDGE/UNDERSTANDING
1. Which statement does not describe an endothermic reaction? (1)
a. The surroundings cool down.
b. ΔH°rxn is positive.
c. Heat is released by the system.
d. Heat is absorbed by the system.
e. The potential energy of the products is greater than the potential energy of the
reactants
2. A chemical reaction is carried out in a coffee cup calorimeter. The temperature of
the water changes from 25.2 °C to 19.8 °C. Which statement is correct? (1)
a. The water loses energy, so the reaction is exothermic.
b. The water gains energy, so the reaction is exothermic.
c. The water loses energy, so the reaction is endothermic.
d. The water gains energy, so the reaction is endothermic.
3. The reaction 2 CO(g) + O2 (g) → 2 CO2 (g) is exothermic. (3)
a. What is the sign of Δ H for this reaction?
i. The sign of ΔH for the exothermic reaction 2 CO(g) + O2(g) → 2 CO2(g) would
be negative
b. Draw an enthalpy diagram for this reaction.
i.
c. What is the sign of Δ H for the reverse reaction?
i. For the reverse reaction, which would be the conversion of 2 CO2(g) into 2 CO(g)
+ O2(g), the sign of ΔH would be the opposite of the forward reaction. Since the
forward reaction is exothermic (ΔH < 0), the reverse reaction would be
endothermic (ΔH > 0) (positive). In an endothermic reaction, heat is absorbed
from the surroundings, resulting in an increase in the enthalpy of the system.
4. Describe two ways in which temperature affects the rate of reaction? (2)
a. Firstly, when the temperature rises, all of the molecules involved in the reaction start to
gain more energy and move faster. This increased energy and speed lead to frequent
collisions between the reacting molecules. The more collisions occur, the higher the
chances of successful collisions, where the molecules collide with enough energy to
break bonds and form new ones. As a result, the reaction rate increases with temperature
due to the increased collision frequency.
b. Secondly, higher temperatures also make collisions more energetic. When molecules
collide with sufficient energy, they can overcome the activation energy barrier required
for the reaction to occur. Activation energy is the minimum energy needed for a chemical
reaction to start. By increasing the temperature, more molecules possess the necessary
energy to surpass this barrier, leading to a greater proportion of successful collisions.
5. What is the difference between specific heat capacity and heat capacity? (2)
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