**31.** An amount of ice of mass \( 10^{-3} \, \text{kg} \) and temperature \( -10^\circ \text{C} \) is transformed to vapour of temperature \( 110^\circ \text{C} \) by applying heat. The total amount of work required for this conversion is: (Take: Specific heat of ice = \( 2100 \, \text{Jkg}^{-1}\text{K}^{-1} \), Specific heat of water = \( 4180 \, \text{Jkg}^{-1}\text{K}^{-1} \), Specific heat of steam = \( 1920 \, \text{Jkg}^{-1}\text{K}^{-1} \), Latent heat of ice = \( 3.35 \times 10^5 \, \text{Jkg}^{-1} \), Latent heat of steam = \( 2.25 \times 10^6 \, \text{Jkg}^{-1} \)) Options: - (1) 3022 J - (2) 3043 J - (3) 3003 J - (4) 3024 J
Detailed Explanation
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Simple Explanation (ELI5)
🧊➡️💧➡️💨 Turning ice-cold ice into hot steam
Imagine you have a tiny ice cube that is really cold ( −10 °C ). You want to turn it into hot steam ( 110 °C ).
To do that you must keep adding heat while the ice passes through several stages:
- Warm the ice so it is not so cold.
- Melt the ice into water — this needs extra energy called latent heat.
- Warm the water up to boiling point.
- Boil the water into steam — again a latent heat step.
- Warm the steam a little more.
Add the energy for every step and you get the total heat you must supply.
Because the ice piece is very tiny (only 1 g), the final answer is only about 3 kilo-Joules of energy.
Step-by-Step Solution
Given Data
Mass:
Specific heats
Ice:
Water:
Steam:
Latent heats
Fusion (ice):
Vaporisation (steam):
Temperature changes
Ice:
Water:
Steam:
Step-wise Heat Calculations
-
Warm the ice
-
Melt the ice
-
Warm the water
-
Vaporise the water
-
Warm the steam
Total Heat / Work Required
Q_{\text{total}} &= Q_1 + Q_2 + Q_3 + Q_4 + Q_5 \\[4pt] &= 21 + 335 + 418 + 2250 + 19.2 \\[4pt] &= 3043.2\,J \approx 3043\,J \end{aligned}$$ **Therefore, the required work/heat is closest to option (2) 3043 J.**Examples
Example 1
Pressure cookers: more energy is needed to convert water to steam at higher boiling points.
Example 2
Meteorology: Large latent heat of water drives storm formation when moist air condenses.
Example 3
Refrigerators: Reverse process—removing latent heat to freeze water into ice.
Example 4
Steam engines: Phase change energy is converted into mechanical work.