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Initially, 2.2 g of pure CO2(g) is sealed in an empty 5 dm³ container at 900 °C - NSC Physical Sciences - Question 6 - 2016 - Paper 2
Question 6
Initially, 2.2 g of pure CO2(g) is sealed in an empty 5 dm³ container at 900 °C. 6.1 Calculate the initial concentration of CO2(g). 6.2 Give a reason why equilibri... show full transcript
Worked Solution & Example Answer:Initially, 2.2 g of pure CO2(g) is sealed in an empty 5 dm³ container at 900 °C - NSC Physical Sciences - Question 6 - 2016 - Paper 2
Step 1
6.1 Calculate the initial concentration of CO2(g).
Answer
To calculate the initial concentration of CO2(g), we use the formula:
Where:
- is the concentration in mol/dm³,
- is the number of moles,
- is the volume in dm³.
First, we convert grams of CO2 to moles:
Given the volume of the container is 5 dm³:
Step 2
6.2 Give a reason why equilibrium will not be established.
Answer
Equilibrium cannot be established because the reaction requires both reactants (CO2 and CaCO3) to be present. If there is only CO2 in the container, the reverse reaction cannot take place and thus equilibrium conditions cannot be met.
Step 3
6.3 Give a reason why this reaction will only reach equilibrium in a SEALED container.
Answer
This reaction must occur in a sealed container to ensure that no reactants or products escape. If the container is open, CO2 can escape from the system, preventing the system from reaching equilibrium.
Step 4
6.4 Calculate the minimum mass of CaCO3(s) that must be added to the container to achieve equilibrium.
Answer
To establish equilibrium, we need to find the minimum amount of CaCO3 that would produce enough CO2 to reach the equilibrium constant.
Given the equilibrium constant:
Let be the change in concentration at equilibrium. Thus:
From the equation:
Thus we solve for :
Solving gives:
$$\Rightarrow n(CaCO_3) = 4x = 0.016 \ $$m = n \times M = 0.016 | 100 g/mol ≈ 0.4 \, ext{g}$$Step 7
6.6 Is the reaction EXOTHERMIC or ENDOTHERMIC? Fully explain how you arrived at the answer.
Answer
The reaction is ENDOTHERMIC. The equilibrium constant (Kc) increases with temperature, which indicates that the forward reaction is favored at higher temperatures. According to Le Chatelier's principle, if the equilibrium constant increases with an increase in temperature, the reaction must be endothermic, as heat is absorbed during the reaction.