Thermal Energy Review Flashcards

To calculate Gravitational Potential Energy ( $GPE$ ), the formula is: $GPE = mgh$ - Where $m$ represents mass, $g$ represents gravitational acceleration, and $h$ represents height.
To calculate Kinetic Energy ( $KE$ ), the formula is: $\text{KE} = \frac{1}{2} mv^2$ - Where $m$ is mass and $v$ is velocity.
To calculate Thermal Energy ( $Q$ ) associated with temperature changes, the formula is: $Q = mC\Delta T$ - Where $m$ is mass, $C$ is the specific heat capacity, and $\Delta T$ is the change in temperature.
To calculate Phase Change Energy ( $Q$ ), use the formula: $Q = mL$ - Where $L$ is the latent heat (either heat of fusion or heat of vaporization).

Conduction: Heat transfer that occurs through direct physical contact. This usually involves solids. - Example: Touching a hot object, or heat moving through a metal rod.
Convection: Heat transfer that occurs through the movement of fluids (liquids and gases). It often involves rotating currents. - Example: The circulation of boiling water in a pot or liquids rotating in a container.
Radiation: Heat transfer through electromagnetic waves, which does not require a medium. - Example: Energy from the sun hitting the earth.

Direction of Heat Transfer: Heat always transfers from a substance with a higher temperature (hot) to a substance with a lower temperature (cold). - Scenario: If a cup of hot water is submerged into a beaker of cold water, heat will transfer from the hot water to the cold water.
Equilibrium State: This transfer of heat will continue until both substances reach thermal equilibrium with one another. At equilibrium, both substances have the same temperature and the net heat transfer is zero.
Molecular Level Mechanics: During conduction, high-energy (faster-moving) molecules collide with lower-energy (slower-moving) molecules, transferring kinetic energy to the cooler substance until the average kinetic energy (temperature) is balanced.

Sensory Perception of Temperature: A tile floor in a bathroom feels colder to bare feet than a bathroom rug, even though both the tile and the rug are at the same room temperature (thermal equilibrium). - The Role of Conductivity: The tile is a conductor. It is more efficient at transferring heat away from your feet via conduction. - Insulation and Specific Heat: The rug is an insulator, meaning it resists heat transfer. Because the tile conducts heat away from the skin rapidly, the rate of kinetic energy loss from the feet is higher, making the tile "feel" colder.
Practical Applications of Insulators: To improve energy efficiency, insulators are used to prevent heat from being lost to surroundings or from entering a cool area. - Common examples include fiberglass insulation in houses or vacuum-sealed layers in thermal flasks.

Definition of Specific Heat: The amount of heat required to raise the temperature of a unit mass of a substance by one degree.
Interpreting Graphical Data: On a graph showing the relationship between heat added and temperature for equal masses of different metals, the line with the smallest slope (the smallest change in temperature for the most heat added) represents the metal with the highest specific heat.
Sample Calculation for Specific Heat: - Given: A $2.0\,kg$ block increases by $5^\circ C$ when $2,000\,J$ of energy are added. - Use $Q = mC\Delta T$ - $2,000\,J = (2.0\,kg) \times C \times (5^\circ C)$ - $2,000 = 10C$ - $C = 200\,J\,kg^{-1}\,^\circ C^{-1}$

Energy Conversion Scenario: Dropping a $4.5\,kg$ wood block from a height of $2.0\,m$ . - This involves converting the initial Potential Energy into Heat upon impact. - $\text{Energy} = mgh = 4.5\,kg \times 9.8\,m/s^2 \times 2.0\,m = 88.2\,J$
Condensation Calculation: Determining the change in thermal energy when $300.0\,g$ of water vapor at $100^\circ C$ condenses. - This requires the formula $Q = mL$ .

Phase Change Points: Phase changes occur at the plateaus (flat horizontal sections) of a temperature-versus-heat graph. - Melting/Freezing Point: For the substance in the diagram, this occurs at $70^\circ C$ . - Boiling/Condensation Point: For the substance in the diagram, this occurs at $140^\circ C$ .
Energy Behavior during Phase Changes: - Kinetic Energy: Changing in segments where the temperature is increasing or decreasing (the sloped lines). - Potential Energy: Changes during the phase changes (the plateaus). From point D to E on the graph (boiling), potential energy increases as the substance transforms from liquid to gas.

Definition of Temperature: Temperature is a measure of the average kinetic energy of the particles within a substance.
Units of Thermal Energy: - Joules ( $J$ ): The standard SI unit for energy. - Calories ( $cal$ ): Commonly used to measure energy content in food.
Comparing Kinetic Energy at Different Temperatures: - Substance A: $60^\circ C$ - Substance B: $300\,K$ ( $300 - 273 = 27^\circ C$ ) - Substance C: $100^\circ F$ ( $\frac{100 - 32}{1.8} \approx 37.7^\circ C$ ) - Conclusion: Gold would have the highest kinetic energy at $60^\circ C$ .

The Principle: The rate of cooling of an object is proportional to the difference in temperature between the object and its surroundings.
Comparison Example: In a room at $21^\circ C$ , a cup of boiling water ( $100^\circ C$ ) will have a greater initial rate of cooling compared to a cup of $50^\circ C$ water because the temperature difference ( $100 - 21 = 79$ ) is larger than the second cup's difference ( $50 - 21 = 29$ ).