Question

The heating curve for 1.0 mole of Na, initially at 25.0°C, is shown above at the left. Which of the following best explains the change in heat when 0.50 mole of Na undergoes the trans a) The heat change is half as much as for 1.0 mole of Na. b) The heat change is the same as for 1.0 mole of Na. c) The heat change is twice as much as for 1.0 mole of Na. d) The heat change cannot be determined from the information provided.

Answer 1

The heat change for 0.50 mole of sodium (Na) during a transition is half as much as for 1.0 mole because enthalpy change is proportional to the number of moles.

Step-by-step explanation:

The question asks about the heat change when 0.5 mole of sodium (Na) undergoes a transition, given that the heating curve is for 1.0 mole of Na initially at 25.0°C. The heat absorbed or released by a substance is directly proportional to the amount of substance, according to the concept of thermochemical equations. Therefore, if 1.0 mole of Na is associated with a certain amount of heat change during the transition, then 0.50 mole will be associated with half that amount of heat change, because the number of moles has been halved.

This understanding is grounded in the concept that enthalpy (ΔH) is an extensive property and changes linearly with the number of moles in a reaction. Hence, the correct answer to the student's question is (a) The heat change is half as much as for 1.0 mole of Na.