Question

The amount of heat required to change liquid water to vapor at its boiling temperature is 2256 kJ/kg. The amount of heat required to change liquid mercury to its vapor state at its boiling temperature is 295 kJ/kg. One kg of each substance is currently at its boiling point.

How will the amount of thermal energy required to change each substance from a liquid to a gas differ?

Water and mercury will require the same amount of energy to change from liquid to gas.

Water will require a greater amount of energy to change from liquid to gas than mercury.

Mercury will require a greater amount of energy to change from liquid to gas than water.

Neither water nor mercury will require any energy to change from liquid to gas as long as they are each at their boiling temperatures.

Answer 1

Water will require a greater amount of energy to change from liquid to gas than mercury.

Step-by-step explanation:

Let's consider the boiling of water.

H₂O(l) → H₂O(g)

At the boiling point, the heat of boiling is 2256 kJ/kg. Given we have 1 kg of water, 2256 kJ of energy will be required.

Let's consider the boiling of mercury.

Hg(l) → Hg(g)

At the boiling point, the heat of boiling is 295 kJ/kg. Given we have 1 kg of water, 295 kJ of energy will be required.

Water will require a greater amount of energy (2256 kJ) to change from liquid to gas than mercury (295 kJ).

Answer 2

2. Water will require a greater amount of energy to change from liquid to gas than mercury.

Step-by-step explanation:

As stated water meeds 2256 kJ/kg to change from liquid to vapor, while mercury only needs 295 kJ/kg.

So the right answer is:

2. Water will require a greater amount of energy to change from liquid to gas than mercury.

If you want to analyze the others:

1. Water and mercury will require the same amount of energy to change from liquid to gas.

This is simply wrong because as I already said the difference in energy is obvious.

3. Mercury will require a greater amount of energy to change from liquid to gas than water.

Mercury requires less than water

4. Neither water nor mercury will require any energy to change from liquid to gas as long as they are each at their boiling temperatures.

When a substance reach its boiling temperature you need to add the required thermal energy, so water and mercury need heat to change to vapor