Question

Calculate the amount of heat energy required to convert 5gram ice at ${0^0}C$ to steam at ${100^0}C$.(In calories)
A) 3100
B) 3200
C) 3500
D) 3600

Answer 1

To convert ice at ${0^0}C$ to steam at ${100^0}C$, we first convert ice into water. Then we increase the temperature of water from ${0^0}C$ to ${100^0}C$ and finally convert water into steam at ${100^0}C$. To convert one gram of ice into water we need 80 calories. To increase ${1^0}C$ temperature of one gram of water we need 1 calorie. To convert one gram of water into steam we need 540 calories.

Complete step by step answer:
Given, 5gram ice at ${0^0}C$.
We know that to convert one gram into water, 80 calories(Latent heat of fusion) of heat required. Then heat energy required to convert 5gram ice into water is given by
${Q_1} = 5 \times 80 = 400C$.
To increase the temperature of one gram of water by ${1^0}C$, 1C heat energy is required. Then heat energy required to increase the temperature of 5gram water from ${0^0}C$ to ${100^0}C$ is given by
${Q_2} = 5 \times 100 \times 1 = 500C$
Similarly, to convert one gram of water into steam we required 540 calories(latent heat of vaporization) of heat energy. Then heat energy required to convert 5gram of water into steam is given by
${Q_3} = 5 \times 540 = 2700C$
Total heat required to convert 5gram ice at ${0^0}C$ to steam at ${100^0}C$is given by
$Q = {Q_1} + {Q_2} + {Q_3}$
$Q = 400 + 500 + 2700 = 3600C$
Hence the correct answer is option D.

Note: If we convert ice into water at any temperature we require the same amount of heat energy. And water converts into steam at any temperature. We require the same amount of energy. If steam converts into water means steam releases energy into its surrounding (only if the surrounding is colder than steam). We always exchange heat energy in an isolated chamber to avoid heat exchange between water and surrounding.