Iron has a smaller heat capacity than water. Suppose that 10 kg of either substance was heated together with 100 kJ of heat for 5 minutes. Which of the following will be TRUE?
Select one: a. Iron would have absorbed more heat b. Iron and water would have the same amount of heat c. Water would have absorbed more heat d. Iron would have a higher temperature than water ÂÂ
Which of the following would lead to an increase in the measured final temperature in the calorimetry of neutralization reactions using a coffee cup calorimeter?
Select one: a. Calorimeter was punctured with a small hole b. Smaller Ccalorimeter c. Smaller number of moles of limiting reactant d. Thermometer was not read right away
The Correct Answer and Explanation is:
Question 1:
Iron has a smaller heat capacity than water. Suppose that 10 kg of either substance was heated together with 100 kJ of heat for 5 minutes. Which of the following will be TRUE?
Options:
- a. Iron would have absorbed more heat
- b. Iron and water would have the same amount of heat
- c. Water would have absorbed more heat
- d. Iron would have a higher temperature than water
Correct answer: d. Iron would have a higher temperature than water
Explanation:
Heat capacity ($C$) is a measure of how much heat energy a substance can absorb per unit change in temperature. More specifically, the specific heat capacity ($c$) is the amount of heat required to raise 1 kg of a substance by 1°C.
- Water has a much higher specific heat capacity (~4.18 kJ/kg·°C).
- Iron has a lower specific heat capacity (~0.45 kJ/kg·°C).
Given the same amount of heat energy (100 kJ) applied to the same mass (10 kg) of each substance:
- Both substances absorb the same amount of heat (100 kJ), so option a and c are incorrect.
- Because water has a higher specific heat capacity, it will increase in temperature less.
- Iron, with its smaller heat capacity, requires less heat to raise its temperature, so its temperature will increase more.
Mathematically:
$$
Q = m c \Delta T \implies \Delta T = \frac{Q}{m c}
$$
Since $Q$ and $m$ are constant, $\Delta T \propto \frac{1}{c}$.
Lower $c$ (iron) → higher $\Delta T$.
Therefore, iron will have a higher final temperature after absorbing the same heat.
Question 2:
Which of the following would lead to an increase in the measured final temperature in the calorimetry of neutralization reactions using a coffee cup calorimeter?
Options:
- a. Calorimeter was punctured with a small hole
- b. Smaller $C_{\text{calorimeter}}$ (heat capacity of the calorimeter)
- c. Smaller number of moles of limiting reactant
- d. Thermometer was not read right away
Correct answer: b. Smaller $C_{\text{calorimeter}}$
Explanation:
In calorimetry, the final temperature change is affected by heat lost or absorbed by the calorimeter itself.
- The heat produced by the neutralization is shared between the solution and the calorimeter.
- The calorimeter has its own heat capacity ($C_{\text{calorimeter}}$) and absorbs some of the heat, reducing the temperature rise observed in the solution.
If the calorimeter’s heat capacity is smaller:
- It absorbs less heat.
- More heat stays in the solution.
- Therefore, the measured final temperature increases.
Now consider the other options:
- a. Calorimeter was punctured with a small hole: This would cause heat loss to the surroundings, lowering the final temperature.
- c. Smaller number of moles of limiting reactant: Less reactant means less heat produced → lower temperature increase.
- d. Thermometer was not read right away: The system would start cooling down by the time the temperature is recorded, leading to a lower measured temperature.
Hence, only a smaller calorimeter heat capacity leads to a higher measured final temperature.
Summary:
| Question | Correct Option | Reason |
|---|---|---|
| Heat absorbed by iron vs. water | d | Both absorb same heat; iron’s lower heat capacity means higher temperature increase |
| Increase final temp in calorimetry | b | Smaller calorimeter heat capacity means less heat absorbed by calorimeter → higher tem |
