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Power, Force and Velocity

A couple sitt...

Question

A couple sitting in a warm room on a winter day takes $\frac{1}{2} kg$ of cheese sandwiches (an energy intake of 8130 kJ for both). Supposing that none of the energy is stored in the body, what mass of water they need to perspire in order to maintain their original temperature?
(Given: Enthalpy of vapourisation of water = 40.65 kJ/mol).

A

3.6 kg

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B

0.028 kg

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C

0.9 kg

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D

0.11 kg

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Solution

The correct option is A 3.6 kg
The heat required for the vaporization of 1 mol i.e., 18 g water is 40.65 kJ
i.e., 40.65 kJ of energy $\equiv 18 g of H_{2} O$
$∴$ 8130 kJ of energy $\equiv \frac{18}{40.65} \times 8130$

$= 3600 g H_{2} O = 3.6 kg H_{2} O$

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