Thermochemistry

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System Noun

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[sis-tuhm]

Back

A specific part of the universe on which attention is focused for study, separate from its surroundings.

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Example: The Earth and Moon form a system where the force of gravity keeps the Moon in a predictable orbit around the Earth.

Front

Surroundings Noun

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[suh-round-ings]

Back

Everything in the universe that is not part of the specific system being studied or observed.

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Example: In science, a 'system' is the specific part of the universe being studied, and the 'surroundings' is everything outside that system's boundary.

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Heat Noun

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[heet]

Back

Energy that transfers from a warmer object to a cooler object because of a temperature difference between them.

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Example: This diagram shows that heat is energy that flows from a hot object (red block) to a cold object (blue block).

Front

Work Noun

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[wurk]

Back

The transfer of energy to or from a system through the application of a force, such as pushing or pulling.

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Example: A person does work by applying a force (pushing) to move an object over a distance, as shown by the arrow.

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Collision Theory Noun

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[kuh-lizh-uhn thee-uh-ree]

Back

A model explaining that chemical reactions occur when reactant particles collide with sufficient energy and the correct orientation.

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Example: This image shows two particles moving toward each other to collide, representing the first step required for a chemical reaction to occur.

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Activated Complex Noun

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[ak-tuh-vey-tid kom-pleks]

Back

An unstable, temporary arrangement of atoms that exists at the peak of the activation energy barrier during a reaction.

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Example: A diver at the peak of their jump represents the activated complex, the temporary, high-energy state between the start (reactants) and end (products) of a reaction.

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Internal Energy Noun

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[in-tur-nl en-er-jee]

Back

The total kinetic and potential energy of all the particles contained within a thermodynamic system.

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Example: The image shows how particles move faster in a hotter object, representing higher internal energy compared to a cooler object.

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Enthalpy (ΔH) Noun

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[en-thal-pee]

Back

A thermodynamic quantity representing the total heat content of a system, measured as the heat absorbed or released at constant pressure.

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Endothermic Process Noun

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[en-doh-thur-mik pros-es]

Back

A chemical or physical process that absorbs heat energy from its surroundings, resulting in a positive enthalpy change (ΔH).

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Example: This shows an endothermic process where a chemical reaction in a test tube absorbs heat energy from its surroundings, represented by the inward-pointing arrows.

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Exothermic Process Noun

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[ek-soh-thur-mik pros-es]

Back

A chemical or physical process that releases heat energy into its surroundings, resulting in a negative enthalpy change (ΔH).

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Example: A campfire is an exothermic process because the combustion of wood releases energy in the form of heat and light, which you can feel and see.