AP Chemistry Flashcards: Introduction to Enthalpy of Reaction
Written by AP Content Team, Verified for 2026 AP Exams, Last updated: May 2026
Review key ideas with interactive flashcards. This set includes 10 cards to help you master important concepts.
Define an endothermic reaction.
An endothermic reaction is a process in which thermal energy is transferred from the surroundings into the chemical system.
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Define an endothermic reaction.
An endothermic reaction is a process in which thermal energy is transferred from the surroundings into the chemical system.
What is the enthalpy change of a reaction (ΔH)?
It is the amount of heat energy released or absorbed by a chemical reaction when it occurs at a constant pressure.
If an endothermic reaction occurs in a test tube, what would you feel when you touch it?
The test tube would feel cold because the reaction is absorbing thermal energy from its surroundings, which includes the test tube and your hand.
What does a negative ΔH value signify about a reaction?
A negative ΔH indicates that the reaction is exothermic, meaning heat energy is released from the system into the surroundings.
Under what specific condition is the heat absorbed or released by a system (q) equal to its enthalpy change (ΔH)?
The heat absorbed or released by a system is equal to the enthalpy change (ΔH) when the chemical reaction is carried out at constant pressure.
How does the change in chemical potential energy during a reaction manifest as an observable change?
The change in chemical potential energy results in a change in the kinetic energy of the system and surroundings, which manifests as a measurable temperature change.
Define an exothermic reaction.
An exothermic reaction is a process in which thermal energy is transferred from the chemical system to the surroundings.
How can you calculate the heat (q) transferred in a reaction using molar enthalpy?
The heat (q) can be calculated by multiplying the amount of the reacting substance in moles by the molar enthalpy of reaction (ΔH).
What does a positive ΔH value signify about a reaction?
A positive ΔH indicates that the reaction is endothermic, meaning heat energy is absorbed by the system from the surroundings.
What is the fundamental cause of the enthalpy change in a chemical reaction?
The enthalpy change is caused by the difference in chemical potential energy between the products and reactants, which arises from the energy changes associated with breaking and forming chemical bonds.