Enthalpy

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Thermodynamics Noun

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[thur-mo-dy-nam-iks]

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Thermodynamics

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The branch of science concerned with heat and temperature and their relation to energy and work in physical systems.

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Example: This diagram shows how adding heat energy (enthalpy) to water changes its state from solid ice to liquid water and then to gaseous steam.

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Thermochemistry Noun

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[thur-mo-kem-iss-tree]

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Thermochemistry

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The study of heat energy associated with chemical reactions and physical transformations, focusing on energy changes during these processes.

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Example: This image shows a chemical reaction in a test tube absorbing energy from its surroundings, represented by the arrows pointing inward, illustrating an endothermic process.

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System Noun

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[sis-tuhm]

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System

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The specific part of the universe that is of interest for study, separated from its surroundings by a boundary.

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Example: In science, a 'system' is the specific part of the universe being studied, separated from the 'surroundings' by a 'boundary'.

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Surroundings Noun

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[suh-round-ings]

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Surroundings

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Everything external to a defined thermodynamic system with which the system can exchange energy and/or matter.

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Example: The 'system' is the chemical reaction (in the beaker), while the 'surroundings' is everything outside it, like the air, which exchanges heat.

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Heat (q) Noun

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[heet]

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Heat (q)

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The transfer of thermal energy between objects due to a temperature difference, typically flowing from a warmer to a cooler body.

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Example: The diagram shows heat flowing from a hot object to a cold object, demonstrating that heat is the transfer of thermal energy due to a temperature difference.

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Temperature Noun

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[tem-per-uh-cher]

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Temperature

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A measure of the average kinetic energy of the particles in a substance, indicating its degree of hotness or coldness.

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Example: This thermometer measures temperature, the average kinetic energy of particles, in Celsius and Fahrenheit. Temperature changes are used to calculate changes in enthalpy (heat).

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Enthalpy (H) Noun

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[en-thal-pee]

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Enthalpy (H)

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The total heat content of a system, representing its internal energy plus the product of its pressure and volume.

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Example: This diagram shows enthalpy as the energy level of a chemical system. In an endothermic reaction, products have higher enthalpy than reactants, requiring energy input.

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Enthalpy Change (ΔH) Noun

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[en-thal-pee chainj]

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Enthalpy Change (ΔH)

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The amount of heat absorbed or released during a chemical reaction or physical process occurring at constant pressure.

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Example: This diagram shows an endothermic reaction, where energy is absorbed. The products end up at a higher energy (enthalpy) level than the reactants.

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Exothermic Reaction Noun

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[ek-so-thur-mik ree-ak-shun]

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Exothermic Reaction

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A chemical reaction that releases energy, usually in the form of heat, into the surroundings, resulting in a negative ΔH.

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Example: This diagram of combustion shows that inputs like fuel and oxygen react to release energy, with 'Heat' clearly shown as an output of the reaction.

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Endothermic Reaction Noun

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[en-do-thur-mik ree-ak-shun]

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Endothermic Reaction

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A chemical reaction that absorbs energy, usually in the form of heat, from the surroundings, resulting in a positive ΔH.

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Example: This diagram shows an instant cold pack's contents. Mixing the inner water with the outer ammonium nitrate starts an endothermic reaction that absorbs heat.