How much heat is necessary to change 10 g of water at 30°C into steam at 100°C?
A) 0.07 kcal
B) 0.7 kcal
C) 6.1 kcal
D) 0.67 kcal

Question

Quizplus · Accepted Answer

To convert 10 g of water at 30°C into steam at 100°C, we need to first raise the temperature of water to 100°C and then convert it into steam. The heat required to raise the temperature of water from 30°C to 100°C is calculated using the formula $q = mc\Delta T$, where $m = 10g$, $c = 1 \frac{cal}{g°C}$ (specific heat of water), and $\Delta T = 70°C$. This gives $q = 10g \times 1 \frac{cal}{g°C} \times 70°C = 700 cal = 0.7 kcal$. Then, to convert water at 100°C to steam, we need the heat of vaporization, which is approximately $540 cal/g$ at 100°C. So, the heat required for vaporization is $10g \times 540 \frac{cal}{g} = 5400 cal = 5.4 kcal$. Adding these two amounts, $0.7 kcal + 5.4 kcal = 6.1 kcal$, which is necessary to change 10 g of water at 30°C into steam at 100°C.

How Much Heat Is Necessary to Change 10 G of Water