Q2 V3 A well insulated calorimeter contains 100 ml of water. 0.100 mol of solid calcium chloride (CaCl2) is added to the water and stirred until it has all dissolved. The water was initially at a temperature of 18.00 oC. After all the calcium chloride has dissolved the temperature is 28.00 oC. What is the cause of the temperature change?

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A well-insulated calorimeter with water experiencing a temperature rise indicates that heat was released into the water rather than absorbed. The setup involves 100 mL of water, so the approximate mass is 100 g. The water temperature increases from 18.00 °C to 28.00 °C, a ΔT of +10.00 °C, which corresponds to heat input to the water of q = m c ΔT ≈ (100 g)(4.18 J/g·K)(10 K) ≈ 4.18 × 10^3 J. This positive heat flow into the water must have come from somewhere inside the system, namely the dissolution process of CaCl2.

Option a claims the CaCl2 has a neutral effect on temperature, which would imply no heat exchange; this contradicts the observed 10 °C rise.

Option c suggests the dissolution is endothermic, meaning the system would absorb heat from the water, producing a temperature drop or a smaller rise; that is inconsistent with the data.

Option d states the CaCl2 reacts with water to form a gas that releases heat. While gas formation could occur in some reactions, there is no indication of gas evolution here, and the main observation is a straightforward temperature increase due to dissolution, not a gas-forming process.

Therefore, the observed warming of the water is best explained by the dissolution process releasing heat into the water, i.e., an exothermic dissolution releasing heat to the surroundings, which aligns with the measured temperature rise.

MUF0042 Chemistry Unit 2 - Semester 2, 2025

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