Latent Heat of Vaporisation Calorimetry: Advanced Thermal Practicals for H2 Physics

TL;DR
Feed dry steam into an insulated calorimeter, log mass gain and temperature rise in real time, and compute latent heat using spreadsheet energy balances.
Cross-check the result against an electrical heating run to expose systematic errors like steam quality and heat loss.
The experiment deepens thermal physics understanding and equips students with the uncertainty commentary SEAB expects for Paper 4.

Why Latent Heat Deserves a Fresh Look

• Thermal physics remains a high-weightage topic in the revised 9478 syllabus, yet few centres go beyond specific heat capacity.
• Calorimetry introduces mass measurements, condensation control, and energy-balancing narratives that examiners applaud in top scripts.
• The investigation doubles as a mini research project for scholarship portfolios and Olympiad personal statements.

Apparatus Overview

Experimental Procedure

1. Calibrate sensors. Ice–water bath for the thermometer, zero the balance with the empty calorimeter, and record least counts.
2. Dry the steam. Pass initial steam through a drying trap (salt-packed flask) to minimise entrained water droplets.
3. Start logging. Record baseline water mass m_0 and temperature T_0. Begin data logging before introducing steam.
4. Introduce steam steadily. Insert the delivery tube below water level to maximise condensation efficiency and prevent splashing.
5. Terminate at target temperature. Stop steaming once the calorimeter content reaches 40–45 °C to avoid large heat losses.
6. Compute energy balance. Latent heat L_v = \frac{(m_2 - m_0) c_w (T_f - T_0) + m_c c_c (T_f - T_0)}{m_s}, where m_s is the mass of condensed steam.
7. Run an electrical check. Replace steam with an immersion heater delivering known IV power over the same temperature range to benchmark system losses.

Discussion and Uncertainty Toolkit

• Steam quality: Estimate the dryness fraction by comparing observed L_v with handbook value (water: 2.26\times10^6\text{ J kg}^{-1}); discuss entrained droplets as a systematic.
• Calorimeter constant: Determine heat capacity of the calorimeter using a calibration run with warm water mixing and include in final calculations.
• Heat loss corrections: Apply Newton’s law of cooling using pre- and post-run temperature slopes to refine the latent heat value.
• Measurement precision: Propagate uncertainties from mass (±0.01 g) and temperature (±0.1 °C) using partial derivatives; present them in your conclusion paragraph.

Extension Pathways

• Investigate latent heat at different pressures using a pressure cooker (with appropriate safety supervision) to introduce Clausius–Clapeyron plots.
• Compare steam calorimetry with an electrical heat-pump setup to discuss real-world efficiency and energy markets.
• Offer an Eclat “Thermo Lab Mastery” clinic where students bring raw CSV files for feedback on uncertainty write-ups.
• Cross-link to Specific Heat Capacity — Electrical vs Mixing Methods so learners can contrast two major calorimetry techniques.

References

• Encyclopædia Britannica, Latent heat
• PhET Interactive Simulations, States of Matter: Basics
• PhET Interactive Simulations, Energy Forms and Changes
• Singapore Examinations and Assessment Board, GCE A-Level Examinations practical requirements