Question

How many joules are required to melt 80 grams of ice to water at 0 C?

Answer 1

Explanation:

Its value is 6.02 kj/mol. This means for every mole of ice we melt we must apply 6.02 kj of heat. We can calculate the heat needed with the following equation:

q

=

n

×

Δ

H

where:

q

= heat

n

= moles

Δ

H

= enthalpy

In this problem we would like to calculate the heat needed to melt 35 grams of ice at 0 °C. This problem can be broken into three steps:

1. Calculate moles of water

2. multiply by the enthalpy of fusion

3. Convert kJ to J

Step 1: Calculating moles of water

35

g

×

(

1

m

o

l

18.02

g

)

=

1.94

m

o

l

s

Step 2: Multiply by enthalpy of fusion

q

=

n

×

Δ

H

=

1.94

×

6.02

=

11.678

k

J

Step 3: Convert kJ to J

11.678

k

J

×

(

1000

J

1

k

J

)

=

11

,

678

J

Finally rounding to 2 sig figs (since 34°C has two sig figs) we get

q

=

12

,

000

J

One last note, if the temperature were not 0 °C then the ice would have to be heated in addition to melted. This would be a phase change problem combined with a heat capacity problem.