Thermochemistry Definitions Flashcards
Thermochemistry
The study of the energy changes that accompany physical or chemical changes
Chemical system
A group of reactants and products being studied
Energy
The ability to do work; SI units joules (J)
Work
The amount of energy transferred by a force over a distance; SI units joules (J)
Heat
The transfer of thermal energy from a warm object to a cooler object
Temperature
A measure of the average kinetic energy of entities in a substance
Potential Energy
The energy of a body or system due to its position or composition
Kinetic Energy
The energy of an object due to its motion
Standard State
The most stable form of a substance under standard conditions, 25 degrees and 100 kPa
Standard Enthalpy of Formation (ΔHf0)
energy associated with 1 mole, formed from its elements in standard states
Open System
a system in which both matter and energy are free to enter and leave the system
Potential Energy Diagram
A graphical representation of the energy transferred during a physical or a chemical change
Bond Dissociation Energy
The energy required to break a given chemical bond
Molar Enthalpy Change (ΔHx)
The enthalpy change associated with a physical, chemical, or nuclear change involving 1 mol of a substance; SI units J/mol
Endothermic
absorbing energy from the surroundings
Closed System
a system in which energy can enter or leave, but matter cannot
Surroundings
all matter that is not part of the system
Enthalpy Change (ΔH)
The energy released to or absorbed from the surroundings during a chemical or physical change
Calorimeter
a device that is used to measure thermal energy changes in a chemical or physical change
Isolated System
an ideal system in which neither matter nor energy can move in or out
Calorimetry
the experimental process of measuring the thermal energy change in a chemical or physical change
Exothermic
Releasing energy to the surroundings
Thermal Energy
The total quantity of kinetic and potential energy in a substance
Law of Conservation of Energy
Energy cannot be created or destroyed
Hess’s Law
The enthalpy change for the conversion of reactants to products is the same whether the conversion occurs in one step or several steps
Exothermic Reaction example
Exothermic reaction is where energy is released into the surroundings as indicated by the lower level in the diagram. An example of an exothermic reaction is the burning of a candle where the bonds between hydrocarbons are broken releasing energy as heat into the surroundings
Endothermic Reaction example
Endothermic reaction is when energy is absorbed from the surroundings indicated by the higher energy level. An example is cooking an egg where the pan absorbs the heat from the stove to begin cooking the egg
Exothermic Chemical reaction example
An example of an exothermic chemical reaction is the combustion of magnesium where the product of the chemical reaction is magnesium oxide as energy is released into the surroundings through the combustion
Endothermic Chemical reaction example
An example of an endothermic chemical reaction is the decomposition of water into its elements of hydrogen and oxygen
