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Hot metal is dropped into cool water in an ideal calorimeter. Which relation holds between the two heat values?
AHeat of metal equals heat of water exactly
BHeat of metal equals minus heat of the water
CHeat of metal equals twice the heat of water
DHeat of metal plus heat of water equals the mass
Answer & Solution
Correct answer: B. Heat of metal equals minus heat of the water
1. In an ideal calorimeter no heat is gained or lost by the calorimeter or its surroundings.
2. So the two heat values must add up to zero.
3. Rearranging gives the heat for the metal as minus the heat for the water.
4. The magnitudes are equal, and the minus sign shows the flow directions are opposite.
5. Here the metal loses heat so its value is negative, while the water gains heat so its value is positive.
_Source: OpenStax Chemistry (CC BY 4.0), Ch 5 "Thermochemistry", section 5.2 Calorimetry_
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