Let’s use the following equation to determine the amount of heat energy that is required to increase the water’s temperature from 20˚ to 100˚.

Q = mass * specific heat * ∆T

Q = 3 * 4190 * 80 = 1.0056 * 10^6 J

For a stone, ∆T = 550 – 20 = 530

Q = 1 * 800 * 530 = 424,000 J

To determine the number of stones, divide these two numbers.

N = 1.0056 * 10^6 ÷ 424,000

The answer is approximately 2.37 stones. If you use 3 stones, some of the water will boil. I would use 3 stones to make sure that water’s final temperature is 100˚C.

# Native Americans boiled water by adding very hot stones to a leak-tight water vessel.?

What minimum number of 1.0 kg stones at 550 ∘C must be added to a vessel holding 3.0 kg of 20∘C water to bring the water to a boil? Use 800 J/(kg⋅K) for the specific heat of the stones and 4190 J/(kg⋅K) for the specific heat of water.

## 2 Answers

- 10
- t1s = initial temperature of a stone = 550 °C

t2s = final temperature of a stone = 100 °C

t1w = initial temperature of the water = 20 °C

t2w = final temperature of the water = 100 °C

ms = mass of a stone = 1.0 kg

mw = mass of the water = 3.0 kg

cs = specific heat of a stone = 800 J/(kg⋅K)

cw = specific heat of water = 4,190 J/(kg⋅K)

Qs = energy lost by a stone = to be determined

Qw = energy gained by the water = to be determined

n = number of stones needed to boil the water = to be determined

NOTE: Since the temperatures involved are about DIFFERENCES in temperature,

there is no need to convert Celsius temperatures into their Kelvin equivalents.

Qw = mw∙cw∙(t2w - t1w)

Qw = 1,005,600 J Energy gained by the water

Qs = ms∙cs∙(t2s - t1s)

Qs = -360,000 J Energy lost by a stone

n = |Qw| / |Qs|

n = 2.793333333 stones, rounded up to 3 stones20

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