Water at 28.0 °C is sprayed onto 0.208 kg of molten gold at 1063 °C (its melting point). The water boils away, forming steam at 100.0 °C and leaving solid gold at 1063 °C. What is the minimum mass of water that must be used?


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John McCann Profile
John McCann answered

This is a simple equality but you have the equality = 0 when the gold is both melted and solid at the same temperature.

The problem does not admit of a solution if there is no change of temperature in the gold

mass * specific heat * change of temperature = mass * specific heat * temperature

One side of this equality would be zero and that would make the solution negative, which is not possible.

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Lard Ass
Lard Ass commented
Are you an educator John?
John McCann
John McCann commented
I have taught from time to time, but I was, basically, a field biologist for state governments and US governments.

You do not need to be an educator to see this problem is wrong in one very important way.

The way it is set up by the questioner this would result.

0 = (some quantity)X

- some quantity = X

You can't have negative mass and 1063 C - 1063 C = 0, which leaves zero on one side of the equality. Besides that, how could the gold be melted and solid at the same exact temperature?

Otherwise this would have been an easy problem.

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