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15 vocabulary flashcards covering enthalpy, ΔH, system and surroundings, endothermic/exothermic reactions, and energy change representations.
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Enthalpy
The total energy contained in a system (sum of chemical potential energy and kinetic energy), symbolized as H.
ΔH (enthalpy change)
The change in enthalpy during a reaction, ΔH = H(products) − H(reactants); indicates heat absorbed or released at constant pressure.
System
The part of the universe being studied (the reaction mixture and its components) in a chemical change.
Surroundings
Everything outside the system, such as the container, air, and the external environment.
Exothermic reaction
A reaction that releases heat to the surroundings; ΔH is negative.
Endothermic reaction
A reaction that absorbs heat from the surroundings; ΔH is positive.
Chemical potential energy
Energy stored in the chemical bonds of molecules; part of the enthalpy of a system.
Kinetic energy
Energy of motion of particles; increases with temperature and contributes to enthalpy.
Energy profile diagram
A graph showing how energy (enthalpy) changes from reactants to products, illustrating ΔH.
Bond breaking
The process of breaking chemical bonds, which requires energy input (an endothermic step).
Bond forming
The formation of new chemical bonds, which releases energy (contributes to an exothermic change).
H(reactants)
The enthalpy of the reactants—the total energy of the starting substances.
H(products)
The enthalpy of the products—the total energy of the substances formed.
Heat energy
Energy transferred due to a temperature difference between the system and surroundings.
Combustion (exothermic example)
A chemical reaction, such as burning a fuel, that typically releases heat energy (exothermic).