31. An amount of ice of mass 10^-3 kg and temperature -10°C is transformed to vapour of temperature 110°C by applying heat. The total amount of work required for this conversion is: Take: Specific heat of ice = 2100 J/kg·K, Specific heat of water = 4180 J/kg·K, Specific heat of steam = 1920 J/kg·K, Latent heat of ice = 3.35×10^5 J/kg, Latent heat of steam = 2.25×10^6 J/kg. Option 1: 3022 J Option 2: 3043 J Option 3: 3003 J Option 4: 3024 J
Detailed Explanation
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Simple Explanation (ELI5)
What is the question?
We have a teeny-tiny piece of ice (just 1 gram!) that starts out really cold at –10 °C. We keep warming it up until it finally becomes hot steam at 110 °C.
Why is it tricky?
Ice does four different things while warming:
- Gets less cold (–10 °C → 0 °C)
- Melts (turns to water)
- Gets hotter (0 °C → 100 °C as liquid)
- Boils (turns to steam)
- Gets even hotter (100 °C → 110 °C as steam)
Each of these steps needs its own amount of heat. Add all those heats together and you know how much energy ("work" in the question) you have to supply.
That’s all the question is asking: “Add up the heat for each step.”
Step-by-Step Solution
Step-by-Step Calculation
Given:
kg
Constants:
J kg⁻¹ K⁻¹
J kg⁻¹ K⁻¹
J kg⁻¹ K⁻¹
J kg⁻¹
J kg⁻¹
1. Warm ice from –10 °C to 0 °C
2. Melt ice at 0 °C
3. Warm water from 0 °C to 100 °C
4. Vaporise water at 100 °C
5. Warm steam from 100 °C to 110 °C
6. Total Heat (Work) Required
Rounded to the nearest joule,
Hence, the correct option is Option 2: 3043 J.
Examples
Example 1
Cooking: Energy needed to melt frozen butter and then bring it to sizzle in a pan involves both latent heat (melting) and sensible heat (warming).
Example 2
Weather: Heat absorbed by ice-capped lakes during spring thaw combines warming of ice, melting, and subsequent warming of water — same multi-step process.
Example 3
Industrial steam boilers: Water must first be heated, then vaporised, then super-heated for turbines; engineers perform similar heat balance calculations.