At a certain elevation,the boiling point of water is 98.5°C.How much energy is needed to heat 35.0 mL of water from 23.4°C to the boiling point at this elevation? [C_p = 75.38 J/(mol.°C),d = 1.00 g/mL]

Question

Quizplus · Accepted Answer

First, we need to find the amount of energy needed to heat the water from 23.4°C to 98.5°C.
q = mcΔT
q = (35.0 g) (4.184 J/g·°C) (98.5°C - 23.4°C)
q = 11.0 kJ

Next, we need to consider the energy needed to reach the boiling point at this elevation.
ΔHvap = (75.38 J/mol) (18.02 g/mol)
ΔHvap = 1358 J/g
q = (35.0 g) (1.00 g/mL) (1358 J/g)
q = 47.5 kJ

Therefore, the total energy needed is:
qtotal = q1 + q2
qtotal = 11.0 kJ + 47.5 kJ
qtotal = 58.5 kJ

The closest choice is B: 11.0 kJ + 47.5 kJ = 58.5 kJ.

At a Certain Elevation,the Boiling Point of Water Is 98