Question

171 mL of H2O), initially at 82.4°C, is cooled to 0°C. How many moles of ice (at 0°C) can

be melted with the energy given off by water? Be sure that your answer has at least one
decimal place.

Answer 1

1) Energy released from water

List known data

Volume: 171 mL H2O

Initial temperature: 82.4ºC

Final temperature: 0ºC

c=4.184 J/gºC

List unknown data

Energy released:

2) Set the equation

q=mcΔT

3) Change volume into mass

`\text{mass of H}_2O=171mL\cdot(1g)/(1mL)=171gH_2O`

4) Replace known values

`q=(171gH_2O)(4.184(J)/(gºC))(0ºC-82.4ºC)=-58954.23\text{ J}`

The total energy released -58954.23 J

5) The energy required to melt ice

List known data

q= -58954.23 J

ΔH(fus)= 334 J/g

List unknown data

m=

6) Set the equation

q=mΔH(fus)

7) Replace known values

+58954.23 J = m (334 J/g)

8) Solve the equation for m.

`m=\frac{+58954.23\text{ J}}{(334J)/(g)}=176.51g`

9) Find moles

`\text{molesofH}_2O=176.51gH_2O\cdot(1molH_2O)/(18.01g)=9.80molH_2O`