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

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Published July 8, 2025
Physics
Thermodynamics
Calorimetry
Phase Change

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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:

  1. Gets less cold (–10 °C → 0 °C)
  2. Melts (turns to water)
  3. Gets hotter (0 °C → 100 °C as liquid)
  4. Boils (turns to steam)
  5. 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.”

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Step-by-Step Solution

Step-by-Step Calculation

Given:
m=103m = 10^{-3} kg

Constants:
cice=2100c_{\text{ice}} = 2100 J kg⁻¹ K⁻¹
cwater=4180c_{\text{water}} = 4180 J kg⁻¹ K⁻¹
csteam=1920c_{\text{steam}} = 1920 J kg⁻¹ K⁻¹
Lf=3.35×105L_f = 3.35 \times 10^5 J kg⁻¹
Lv=2.25×106L_v = 2.25 \times 10^6 J kg⁻¹


1. Warm ice from –10 °C to 0 °C

Q1=mciceΔT=103×2100×(0(10))=0.001×2100×10=21JQ_1 = m c_{\text{ice}} \Delta T = 10^{-3} \times 2100 \times (0 - (-10)) = 0.001 \times 2100 \times 10 = 21\,\text{J}

2. Melt ice at 0 °C

Q2=mLf=103×3.35×105=3.35×102=335JQ_2 = m L_f = 10^{-3} \times 3.35 \times 10^5 = 3.35 \times 10^{2} = 335\,\text{J}

3. Warm water from 0 °C to 100 °C

Q3=mcwaterΔT=103×4180×100=418JQ_3 = m c_{\text{water}} \Delta T = 10^{-3} \times 4180 \times 100 = 418\,\text{J}

4. Vaporise water at 100 °C

Q4=mLv=103×2.25×106=2250JQ_4 = m L_v = 10^{-3} \times 2.25 \times 10^6 = 2250\,\text{J}

5. Warm steam from 100 °C to 110 °C

Q5=mcsteamΔT=103×1920×10=19.2JQ_5 = m c_{\text{steam}} \Delta T = 10^{-3} \times 1920 \times 10 = 19.2\,\text{J}

6. Total Heat (Work) Required

Qtotal=Q1+Q2+Q3+Q4+Q5=21+335+418+2250+19.2=3043.2JQ_{\text{total}} = Q_1 + Q_2 + Q_3 + Q_4 + Q_5 = 21 + 335 + 418 + 2250 + 19.2 = 3043.2\,\text{J}

Rounded to the nearest joule, Qtotal3043JQ_{\text{total}} \approx 3043\,\text{J}

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.

Visual Representation

References

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