Steam at 100 ∘C100\ ^{\circ}\text{C}100 ∘C can cause a worse burn than the same mass of water at 100 ∘C100\ ^{\circ}\text{C}100 ∘C.
A drop of 2.0 g of steam lands on a person's skin and condenses.
The specific latent heat of vaporisation of water is 2.26 × 106 J/kg.
Use the equation: thermal energy for a change in state=mass×specific latent heat\text{thermal energy for a change in state} = \text{mass} \times \text{specific latent heat}thermal energy for a change in state=mass×specific latent heat
Calculate the energy released when the steam condenses to water at 100 ∘C100\ ^{\circ}\text{C}100 ∘C.
The 2.0 g of water then cools from 100 ∘C100\ ^{\circ}\text{C}100 ∘C to 37 ∘C37\ ^{\circ}\text{C}37 ∘C.
The specific heat capacity of water is 4200 J/kg ∘C4200\ \text{J/kg}\ ^{\circ}\text{C}4200 J/kg ∘C.
Use the equation: change in thermal energy=mass×specific heat capacity×change in temperature\text{change in thermal energy} = \text{mass} \times \text{specific heat capacity} \times \text{change in temperature}change in thermal energy=mass×specific heat capacity×change in temperature
Calculate the energy released as the water cools.
Use your answers to (a) and (b) to explain why steam causes a worse burn than the same mass of water at 100 ∘C100\ ^{\circ}\text{C}100 ∘C.
44 exam-style questions on OCR GCSE Physics 1.2 Changes of state, covering 1.2.1 Conservation of mass during changes of state, 1.2.2 Physical and chemical changes, 1.2.3 Heating, temperature and changes of state, 1.2.4 Specific heat capacity and specific latent heat, 1.2.5 Internal energy and temperature change, and 1.2.6 Energy transfer during a change of state. Each one has a worked solution and a mark scheme showing where the marks go.