Question

Identify the equation used to determine the amount of heat required to melt $10grams$ of ice.

• A. $Q=m{C}_{sp}\Delta T$
• B. $Q=n\Delta H$
• C. $KE=\frac{1}{2}m{v}^2$
• D. $PE=mgh$

Answer 1

Answer: (B)

$Q=n\Delta H$

Correct abbreviation for heat is Q. So we can eliminate choices (C), (D), and (E). During a phase change, the temperature of a substance remains constant. Therefore, choice (A) must be wrong because it has a term for changing temperature, ΔT. In fact, choice (A) is the equation used to determine the change in temperature when heat is added or removed from a substance that isn't undergoing a phase change. Choice (B) is the correct choice, where Q is the heat added or removed, n is the number of moles of substance, and ΔH is the heat of phase change, a quantity that is unique for every substance.