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5.1 Define the term reaction rate - NSC Physical Sciences - Question 5 - 2021 - Paper 2
Question 5
5.1 Define the term reaction rate. 5.2 Give a reason why the gradient of the graph decreases between t2 and t3. 5.3 Changes in the graph between t1 and t2 are du... show full transcript
Worked Solution & Example Answer:5.1 Define the term reaction rate - NSC Physical Sciences - Question 5 - 2021 - Paper 2
Step 1
Step 2
Give a reason why the gradient of the graph decreases between t2 and t3.
Answer
The gradient of the graph decreases between t2 and t3 because the concentration of the reactants is decreasing as the reaction progresses. With less reactant available, the rate of CO2 production slows down, leading to a shallower slope on the graph.
Step 3
Changes in the graph between t1 and t2 are due to temperature changes within the reaction mixture.
Answer
The increase in temperature typically results in an increase in the reaction rate, as higher temperatures provide reactant molecules with greater kinetic energy, accelerating the reaction.
Step 4
Step 5
Explain the answer by referring to the graph.
Answer
The graph shows an increasing volume of CO2 produced, which corresponds to energy release as the reaction occurs. An exothermic reaction indicates that heat is given off, causing the reaction mixture temperature to rise, reflected in the steeper gradient observed between t1 and t2.
Step 6
Calculate the value of X on the graph assuming that the gas is collected at 25 °C. Take the molar gas volume at 25 °C as 24 000 cm³.
Answer
Given the percentage purity of the sample is 82.5% and 15 g of CaCO3 is used, the moles of CaCO3 can be calculated as:
n( ext{CaCO}_3) = rac{15 ext{ g} imes 82.5}{100 ext{ g/mol}} = 0.124 ext{ mol}$$ The total volume of CO2 produced can thus be calculated using:V( ext{CO}_2) = n( ext{CO}_2) imes 24,000 ext{ cm}^3 = 0.124 ext{ mol} imes 24,000 ext{ cm}^3 = 2,976 ext{ cm}^3
Step 7
How will the reaction rate change if 15 g of a PURE sample of CaCO3 reacts with the same HCl solution?
Answer
The reaction rate will INCREASE because using a pure sample of CaCO3 ensures that the full available mass will react with HCl, leading to a greater concentration of reactants and hence a faster rate of reaction, as compared to an impure sample.