Physics · Grades 10–12
Energy for a phase change
At the phase-change temperature, use latent heat rather than a temperature-rise formula.
Rule and assumptions
At the phase-change temperature, use latent heat rather than a temperature-rise formula.
Q = mL
Worked examples
A 400 g sample completely melts at its melting temperature. Its latent heat is 360000 J/kg. Ignore losses. Find energy required. Round to 3 decimal places if needed. Answer in J.
Q = mL (400/1000) × 360000 = 144000
144000 J
A 590 g sample completely melts at its melting temperature. Its latent heat is 200000 J/kg. Ignore losses. Find energy required. Round to 3 decimal places if needed. Answer in J.
Q = mL (590/1000) × 200000 = 118000
118000 J
Try two questions
A 690 g sample completely melts at its melting temperature. Its latent heat is 280000 J/kg. Ignore losses. Find energy required. Round to 3 decimal places if needed. Answer in J.
A 90 g sample completely melts at its melting temperature. Its latent heat is 260000 J/kg. Ignore losses. Find energy required. Round to 3 decimal places if needed. Answer in J.
Answers and reasoning
Answers and marking notes
- 193200 J
Q = mL (690/1000) × 280000 = 193200
- 23400 J
Q = mL (90/1000) × 260000 = 23400
Further reading and review references
These are reference links, not copied exercises, institutional endorsement or proof of independent review.
Learning preview · independent educational and translation review required. Suggested grades are not official curriculum alignment.