Heating curve: where the heat goes
"Heating curve: where the heat goes" is a free, interactive Class 11 Physics simulation for NEET and JEE, built on the lesson "Latent heat" in Thermal Properties of Matter. Choose the mass and slide the heat supplied. Watch the thermometer: sometimes it climbs, sometimes it stops dead while the heat keeps going in. On the sloping parts Q = msΔT and the temperature climbs; on the flat parts Q = mL and only the state changes. Ice climbs faster than water for the same heat because its specific heat is smaller, and the boiling plateau is by far the longest. JEE Main asked 21 questions from this chapter across the 42 shifts Lumi has analysed (2017–2026).
From the lesson Latent heat in Thermal Properties of Matter. Change the values and watch what happens.
In JEE Main
42 shifts analysed
21 questions from Thermal Properties of Matter across the 42 JEE Main shifts Lumi has analysed (2017–2026).
The idea behind it
NCERT §10.8.1
- During a change of state, heat goes in (or out) but the temperature does not change. The heat per unit mass needed for the change is the latent heat L, so Q = mL. Its SI unit is J kg⁻¹, and it depends on pressure.
- L_f, the latent heat of fusion, applies to solid ↔ liquid; L_v, the latent heat of vaporisation, applies to liquid ↔ gas. The same amount of heat is released when the change runs the other way.
- For water at standard pressure: L_f = 3.33 × 10⁵ J kg⁻¹ and L_v = 22.6 × 10⁵ J kg⁻¹. Melting 1 kg of ice at 0 °C takes 3.33 × 10⁵ J; turning 1 kg of water at 100 °C into steam takes 22.6 × 10⁵ J.
- Steam at 100 °C scalds more badly than water at 100 °C: as it condenses on skin it gives up its latent heat of vaporisation as well.
- Melting point, L_f, boiling point, L_v (L in 10⁵ J kg⁻¹): ethanol −114 °C, 1.0, 78 °C, 8.5; gold 1063 °C, 0.645, 2660 °C, 15.8; lead 328 °C, 0.25, 1744 °C, 8.67; mercury −39 °C, 0.12, 357 °C, 2.7; nitrogen −210 °C, 0.26, −196 °C, 2.0; oxygen −219 °C, 0.14, −183 °C, 2.1; water 0 °C, 3.33, 100 °C, 22.6.
- A temperature–heat graph for heating ice to steam has sloping parts (temperature rising, Q = msΔT) and flat parts (state changing, Q = mL). The slope of a sloping part is 1/(ms), so ice rises faster than water for the same heat.
- Worked example: a 0.15 kg block of ice at 0 °C goes into 0.30 kg of water at 50 °C; the mixture settles at 6.7 °C. Heat lost by water = 0.30 × 4186 × 43.3 = 54376.14 J; heat to warm the melted ice = 0.15 × 4186 × 6.7 = 4206.93 J; so 0.15 L_f = 50169.21 J and L_f ≈ 3.34 × 10⁵ J kg⁻¹.
- Worked example: turning a 3 kg ice block that starts at −12 °C into steam at 100 °C, with s_ice = 2100 J kg⁻¹ K⁻¹, s_water = 4186 J kg⁻¹ K⁻¹, L_f = 3.35 × 10⁵ J kg⁻¹, L_steam = 2.256 × 10⁶ J kg⁻¹. Warm ice 75600 J, melt 1005000 J, warm water 1255800 J, boil 6768000 J; total 9104400 J ≈ 9.1 × 10⁶ J.
- In that example boiling alone takes about three-quarters of the total heat, far more than warming the water from 0 °C to 100 °C.
Questions
3 answers
- What does the "Heating curve: where the heat goes" simulation show?
- Choose the mass and slide the heat supplied. Watch the thermometer: sometimes it climbs, sometimes it stops dead while the heat keeps going in.
- Does JEE Main ask questions from Thermal Properties of Matter?
- Yes. JEE Main asked 21 questions from this chapter across the 42 shifts Lumi has analysed (2017–2026).
- Is this simulation free?
- Yes. It is free and runs in the browser on a phone or a laptop. It belongs to the lesson "Latent heat" in Thermal Properties of Matter (Class 11 Physics).
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