Which of the following statements about temperature is correct?
a. Temperature is proportional to the average speed of the molecules
b. When an object changes phase, its temperature always increases
c. Temperature is a measure of both the kinetic and potential energies of the constituent molecules
d. None of the above
The correct answer and explanation is:
The correct answer is a. Temperature is proportional to the average speed of the molecules.
Explanation:
Temperature is a measure of the average kinetic energy of the molecules in a substance. This kinetic energy is directly related to the speed of the molecules. The faster the molecules move, the higher the temperature. This is because the kinetic energy of a molecule is given by the equation: KE=12mv2KE = \frac{1}{2} m v^2
where mm is the mass of the molecule, and vv is its velocity. The temperature of a substance is thus proportional to the average speed of the molecules in the substance. In a gas, for example, the higher the temperature, the faster the molecules move on average.
Let’s evaluate the other options to clarify why they are incorrect:
b. When an object changes phase, its temperature always increases.
This statement is false because when a substance undergoes a phase change, such as from solid to liquid (melting) or from liquid to gas (vaporization), the temperature of the substance does not always increase. For example, when ice melts into water, the temperature remains constant at 0°C (at standard pressure) until all the ice has melted. Similarly, during the boiling of water, the temperature stays at 100°C until all the liquid has turned into gas.
c. Temperature is a measure of both the kinetic and potential energies of the constituent molecules.
This statement is partially true but not entirely accurate when considering the definition of temperature. Temperature specifically measures the average kinetic energy of the molecules. Potential energy, such as the energy stored in the bonds of molecules, does not directly contribute to temperature. Changes in potential energy, like when molecules are rearranged during phase changes, can affect the state of matter but not the temperature directly.
Therefore, option a is the most accurate description of temperature.