19.11:
Heat Capacity: Problem-Solving
Consider a metal cylinder containing 160 grams of oxygen gas with a molar mass of 16 g/mol in a room at 25.0 degrees Celsius. The cylinder is moved and kept outside the room on a hot summer day.
The oxygen gas in the cylinder comes into equilibrium with the surrounding temperature, as 600 J of heat is conducted through the cylinder walls. Ignoring the expansion of the metal cylinder, determine the equilibrium temperature.
To solve the problem, first, identify the known and unknown quantities.
Next, the number of moles can be determined by dividing the mass of the gas by its molar mass.
Recall the molar heat capacity equation at constant volume.
Oxygen is a diatomic gas; by substituting the degree of freedom, the equation of molar heat capacity for an ideal diatomic gas at a constant volume can be obtained.
Lastly, by rearranging the equation and substituting the values, the temperature change is determined to be 2.88 degrees Celsius, and the equilibrium temperature to be 27.88 degrees Celsius.
19.11:
Heat Capacity: Problem-Solving
The heat capacity of a gas is the amount of heat energy required to raise the temperature of a unit mass of gas by one degree Celsius. It is an important thermodynamic property of gases, and its determination is essential in many industrial and scientific applications. Here are the steps to solve problems related to the heat capacities of gases:
Determine the type of gas: The heat capacity of a gas depends on its molecular structure and the degree of freedom of its molecules. Different types of gases have different heat capacities, and their values can be obtained from tables or empirical equations.
Calculate the specific heat capacity: A gas's specific heat capacity (c) is the amount of heat energy required to raise the temperature of a unit mass of the gas by one degree Celsius. It can be calculated using the equation:
where M is the molar mass of the gas.
Determine the degree of freedom of the gas: In a dynamic system, the degree of freedom of a gas molecule is the number of directions in which it can move. It depends on the molecular structure and the number of atoms in the molecule. The degree of freedom determines the value of the heat capacity of the gas. For example, a monatomic gas like helium has only three degrees of freedom, whereas a diatomic gas like oxygen has five degrees of freedom.
Calculate the heat capacity at constant volume: The heat capacity at constant volume (CV) is the amount of heat energy required to raise the temperature of one mole of a gas by one degree Celsius at constant volume. It can be calculated using the equation:
where d is the degree of freedom of the gas and R is the gas constant.
Calculate the heat capacity at constant pressure: A gas's heat capacity at constant pressure (CP) is the amount of heat energy required to raise the temperature of one mole of the gas by one degree Celsius at constant pressure. It can be calculated using the equation:
Finally, determining the heat capacities of gases requires a combination of experimental measurements, empirical equations, and thermodynamic calculations. The values of the heat capacities depend on the molecular structure and the degree of freedom of the gas. They play a crucial role in many scientific and engineering applications.
Suggested Reading
- Young, H.D. and Freedman, R.A. (2012). University Physics with Modern Physics. San Francisco, CA: Pearson. Pp.
- OpenStax. (2019). University Physics Vol. 1. [Web version]. Retrieved from https://openstax.org/books/university-physics-volume-2/pages/2-3-heat-capacity-and-equipartition-of-energy