Thermal energy added or removed from a substance that changes the state of the substance is called

Step 1: Analyze the question The question asks for the name of the thermal energy that is added to or removed from a substance while it changes its state (for example, solid to liquid, or liquid to gas).

Step 2: Explain the concept When a substance melts, boils, freezes, or condenses, the heat supplied or removed does not change its temperature. It goes into breaking or forming the bonds between particles. This hidden heat is called latent heat.

• Latent heat of fusion: heat needed to change a solid to a liquid (or released when a liquid freezes) at constant temperature.
• Latent heat of vaporization: heat needed to change a liquid to a gas (or released when a gas condenses) at constant temperature.

The formula is Q = mL, where m is the mass and L is the specific latent heat.

Step 3: Check each option

• A. Latent heat: correct. It is the heat absorbed or released during a change of state at constant temperature.
• B. Heat of reaction: this is the heat change in a chemical reaction, not a physical change of state.
• C. Calorimetry: this is the method of measuring heat quantities, not a type of energy.
• D. Specific heat: this is the heat needed to raise the temperature of 1 kg of a substance by 1 K (Q = mcΔθ). It involves a temperature change, not a change of state.

Step 4: Answer The correct option is A. latent heat.

Tip: "Latent" means hidden. During a change of state the thermometer reading stays constant, so the heat seems to "hide." Specific heat goes with a temperature change (Q = mcΔθ), while latent heat goes with a change of state (Q = mL).