College

As a 5.00-kg sample of liquid mercury is cooled into a solid, it liberates 157 kJ of energy. What is the original temperature of the mercury?

For mercury:
- Melting point: 234 K
- Heat of fusion: 11.3 kJ/kg
- Specific heat: 140 J/(kg·K)

Possible answers:
A. 378 K
B. 690 K
C. 157 K
D. 410 K

Answer :

The original temperature of the mercury is 260.6K

Here is how to arrive at temperature of the mercury

To solve this problem, we can use the formula for the heat released during the solidification of a substance:

Q = m * Lf

where Q is the heat released, m is the mass of the substance, and Lf is the heat of fusion of the substance.

In this case, Q = 157 kJ, m = 5.00 kg, and Lf = 11.3 kJ/kg.

We also need to use the formula for the heat absorbed or released during a temperature change:

Q = m * c * ΔT

where Q is the heat absorbed or released, m is the mass of the substance, c is the specific heat of the substance, and ΔT is the change in temperature.

We can use this formula to calculate the heat released as the mercury cools from its original temperature to its melting point, and then use the formula for solidification to calculate the heat released as the mercury solidifies.

Let T be the original temperature of the mercury.

The heat released as the mercury cools from its original temperature to its melting point is:

Q1 = m * c * (T - 234)

The heat released as the mercury solidifies is:

Q2 = m * Lf

The total heat released is:

Q = Q1 + Q2 = m * c * (T - 234) + m * Lf

Substituting the values given in the problem, we get:

157 kJ = 5.00 kg * 140 J/kg . K * (T - 234) + 5.00 kg * 11.3 kJ/kg

Simplifying and solving for T, we get:

T = 260.6 K

Therefore, the original temperature of the mercury was 260.6 K.

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