Question

A sample of 1.59 grams of Z is dissolved into 500 grams of water which is in a styrofoam coffee cup. The temperature is monitored and is found to drop from 23.669◦C to 23.384◦C. What is ∆Hsolution for substance Z? Assume no heat is lost/gained by the cup itself. The specific heat of water is 4.184 J/g· ◦C and the molecular weight of Z is 131 g/mol. Answer in units of kJ/mol of Z.

Answer 1

Answer: 49.27 kJ / mol

Explanation:

moles of Z = 1.59/131 = 0.0121

Energy absorbed by water = mass x heat capacity x temp difference

= 500 x 4.184 x 0.285 J = 596.2

Divide by 1000 to convert J to kJ = 0.5962 kJ

To get value per mole, now divide by no of moles. = 49.27 kJ/mol