The Foundations of Chemistry

Number of joules gained by water
(247 g)4.18 (10.9°C)

Let x
specific heat of iron

Number of joules lost by iron
(385 g)x (65.9°C)

We set these two quantities equal to one another and solve for x.

(247g)4.18 (10.9°C)
(385 g)x (65.9°C)

x

0.444

You should now work Exercise 58.

The specific heat of iron is much smaller than the specific heat of water.

0.106

The amount of heat required to raise the temperature of 205 g of iron by 70.2°C (as we
calculated for water in Example 1-18) is

Amount of heat
(205 g)(70.2°C)
6.39 103 J, or 6.39 kJ

We see that the amount of heat required to accomplish a given change in temperature
for a given quantity of iron is less than that for the same quantity of water, by the same
ratio.

0.106

It might not be necessary to carry out explicit calculations when we are looking only
for qualitative comparisons.

EXAMPLE 1-20 Comparing Specific Heats

We add the same amount of heat to 10.0 grams of each of the following substances starting at
20.0°C: liquid water, H 2 O(
); liquid mercury; Hg(
); liquid benzene, C 6 H 6 (
); and solid alu-
minum, Al(s). Rank the samples from lowest to highest final temperature. Refer to Appendix
E for required data.

Plan

We can obtain the values of specific heats (Sp. Ht.) for these substances from Appendix E. The
higher the specific heat for a substance, the more heat is required to raise a given mass of sam-
ple by a given temperature change, so the less its temperature changes by a given amount of
heat. The substance with the lowest specific heat undergoes the largest temperature change,
and the one with the highest specific heat undergoes the smallest temperature change. It is not
necessary to calculate the amount of heat required to answer this question.

6.39 kJ



60.2 kJ

Number of joules required to warm 205 g of iron by 70.2°C



Number of joules required to warm 205 g of water by 70.2°C

0.444 J



g°C

0.444 J/g°C



4.18 J/g°C

Specific heat of iron



Specific heat of water

J



g°C

(247 g)4.18 

g

J

°C

(10.9°C)



(385 g)(65.9°C)

J



g°C

J



g°C

J



g°C

J



g°C

1-13 Heat Transfer and the Measurement of Heat 39