Exercises: Energy, heat and work

In a lab experiment, an aluminum block of mass $m = 150.0\,\text{g}$ is heated from an initial temperature of $18.0\,^{\circ}\text{C}$ to $68.0\,^{\circ}\text{C}$. Given that the specific heat capacity of aluminum over this range is $c = 0.897\,\text{J}\times\text{g}^{-1}\times\text{K}^{-1}$ and assuming that heat losses to the surroundings are negligible:

1. a) Calculate the quantity of heat absorbed by the metal block, expressed in joules and in kilojoules.
2. b) Justify conceptually why the heat absorbed is not an intrinsic property possessed by the block, clearly distinguishing between heat and temperature.

In a constant-pressure mixing calorimeter whose own heat capacity is negligible, $250.0\,\text{g}$ of liquid water at a temperature of $20.0\,^{\circ}\text{C}$ are introduced. Next, a metal piece of mass $80.0\,\text{g}$, taken from an oven at $95.0\,^{\circ}\text{C}$, is added. The mixture is stirred until a thermal equilibrium temperature of $24.2\,^{\circ}\text{C}$ is reached. Data: specific heat capacity of liquid water $c_{\text{agua}} = 4,184\,\text{J}\times\text{g}^{-1}\times\text{K}^{-1}$. Assume that there are no heat losses to the surroundings.

1. a) Set up the calorimetry balance and determine the specific heat capacity of the metal, expressed in $\text{J}\times\text{g}^{-1}\times\text{K}^{-1}$.
2. b) If a small heat loss to the surroundings had occurred during the experiment, explain whether the experimental value obtained for the specific heat capacity of the metal would be greater or less than the true value.