Question

1. A 74.20 kg piece of copper metal is heated from 21.5°C to 335.1°C. Calculate the heat absorbed (in kJ) by the metal.

2. A sheet of gold weighing 10.9 g and at a temperature of 17.3°C is placed flat on a sheet of iron weighing 23.9 g and at a temperature of 52.2°C. What is the final temperature of the combined metals? Assume that no heat is lost to the surroundings. (Hint: The heat gained by the gold must be equal to the heat lost by the iron.)

3. A 0.1145-g sample of solid magnesium is burned in a bomb calorimeter that has a heat capacity of 1769 J/°C. The calorimeter contains exactly 301 g of water, and the temperature increases by 1.126°C. Calculate the heat given off by the burning Mg, in kJ/g and in kJ/mol.

4. A 43-kg person drinks 510. g of milk, which has a "caloric" value of approximately 3.0 kJ/g. If only 17% of the energy in milk is converted to mechanical work, how high (in meters) can the person climb based on this energy intake? [Hint: The work done in ascending is given by mgh, where m is the mass (in kilograms), g the gravitational acceleration (9.8 m/s²), and h the height (in meters.)]

Answer 1

1.Sol:-

We know that

Heat absorbed by Cu (q) = mass of Cu (m) x specific heat capacity of Cu (C_s ) x Change in temperature (delta T). .................(1)

Given

Mass of Cu (m) = 74.20 kg = 74200 g

Change in temperature (delta T ) = T₂ - T₁ = 335.1 ⁰C - 21.5 ⁰C = 313.6 ⁰C

Note that Specific heat capacity of Cu (C_s) = 0.385 J g^-10C^-1

Now from equation (1), we have

Heat absorbed by Cu (q) = 74200 g x 0.385 J g^{-1 0}C^-1 x 313.6 ⁰C

= 8958611.2 J  

= 8958.6 KJ

Hence Heat absorbed by Cu = 8958.6 KJ