Question

What is the total energy needed to boil 255 grams of water, given that the

ΔH vaporization= 40,650 J/mol

Answer 1

• 575,000 J

Step-by-step explanation:

1) Convert the mass of water into number of moles

• Molar mass of water: 18.015 g/mol

• Number of moles, n = mass in grams / molar mass

n = 255 g / 18.015 g/mol = 14.15 mol

2) Use the formula E = n × ΔH vap

This is, you have to multiply the molar ΔH vaporization by the number of moles to find the total energy to boil the given amount of water.

• E = 14.15 mol × 40,650 J/mol = 575,395.5 J

3) Round to the correct number of significant figures.

The mass of water is the measurement with the least number of significant figures (3), so you must report the answer with 3 significant figures,

• E = 575,000 J ← answer