Energy in Chemical Bonds

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Collision Theory Noun

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

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Collision Theory

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

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Example: This diagram shows that for a chemical reaction to happen, molecules must collide with enough energy and in the correct orientation to form new products.

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Activated Complex Noun

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

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Activated Complex

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

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Example: This graph shows that for a chemical reaction to happen, reactants must gain enough energy to reach a high-energy, unstable state called the activated complex.

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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 being studied or on which attention is focused in an experiment.

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

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Surroundings Noun

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[suh-roun-dingz]

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Surroundings

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Everything in the universe that exists outside of the specific part being studied, which is known as the system.

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Example: In science, the 'surroundings' is everything outside of the 'system' being studied. Together, the system and surroundings make up the universe.

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Heat Noun

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[heet]

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Heat

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The transfer of thermal energy from a warmer object to a cooler object due to a difference in temperature.

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Example: This diagram shows a combustion reaction, where a hydrocarbon (like wood or coal) reacts with oxygen to release energy in the form of heat and light.

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Internal Energy Noun

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

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Internal Energy

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The total energy contained within a system, which includes the kinetic and potential energy of all its constituent particles.

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Example: Internal energy is the total energy of a substance, which includes the kinetic energy from the movement of its molecules and the potential energy stored in the bonds between them.

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Enthalpy (ΔH) Noun

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[en-thal-pee]

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Enthalpy (ΔH)

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A thermodynamic quantity representing the total heat content of a system, where its change is the heat exchanged at constant pressure.

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Example: This image shows that energy (heat) must be added to water to change its state from ice to liquid and then to steam, illustrating an enthalpy change.

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Bond Enthalpy Noun

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[bond en-thal-pee]

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Bond Enthalpy

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The amount of energy required to break one mole of a specific type of chemical bond in the gaseous state.

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Example: This diagram shows that energy is used to break the chemical bonds in reactants, and energy is released when new bonds form in the products.

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Endothermic Process Noun

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

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Endothermic Process

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A chemical process or reaction that absorbs energy from its surroundings, typically in the form of heat.

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Example: This image shows arrows pointing inward toward a test tube, representing a chemical process that absorbs energy from its surroundings.

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Exothermic Process Noun

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

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Exothermic Process

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A chemical process or reaction that releases energy into its surroundings, typically in the form of heat or light.

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Example: Burning wood (a combustion reaction) is an exothermic process because it releases energy from chemical bonds in the wood and oxygen as heat and light.