Energetics Definitions Flashcards
Heat
A form of energy that flows from something at a higher temperature to something at a lower temperature
Temperature
A measure of the average kinetic energy of particles
Internal energy
The total amount of energy (kinetic and potential) in a sample of a substance
Exothermic
Heat energy is transferred from the system (chemical reaction) to the surroundings - surroundings get hotter
Endothermic
A system (chemical reaction) takes in heat energy from the surroundings - surroundings get cooler
Enthalpy change
The heat energy exchanged with the surroundings at constant pressure
Stability
Refers to the relative energies of the reactants and products. If the products are at a lower enthalpy than the reactants, then they are more stable
Standard conditions
A common set of conditions used to compare enthalpies: 100kPa, 1mol/dm3, 298K if not specified
Standard enthalpy change of reaction
The enthalpy change when molar amounts of reactants, as shown stoichiometric equation, react together under standard conditions
Standard enthalpy change of combustion
The enthalpy change when one mole of a substance is burnt completely in oxygen under standard conditions
Specific heat capacity
The energy needed to raise the temperature of 1g of a substance by 1K (1°C)
Enthalpy change of neutralisation
Enthalpy change when one mole of water molecules are formed when an acid (H+) reacts with an alkali (OH-) under standard conditions
Enthalpy change of solution
The enthalpy change when one mole of a solute is dissolved in excess solvent to form a solution of infinite dilution under standard conditions
Hess’ Law
The enthalpy change accompanying a chemical reaction is independent of the pathway between initial and final states
Standard enthalpy change of formation
The enthalpy change when one mole of a substance is formed from is elements in their standard states under standard conditions
Standard state
The pure substance at 100kPa and a specified temperature (298K if not specified)
Bond enthalpy
The enthalpy change when one mole of covalent bonds in a gaseous molecule are broken under standard conditions
Standard enthalpy change of vaporisation
The energy needed to convert one mole of a liquid into vapour under standard conditions
Average bond enthalpy
The average amount of energy required to break one mole of covalent bonds in gaseous molecules under standard conditions
First ionisation energy
The enthalpy change when one electron is removed from each atom in one mole of gaseous atoms under standard conditions
First electron affinity
The enthalpy change when one electron is added to each atom in one mole of gaseous atoms under standard conditions
Lattice enthalpy
The enthalpy change when one mole of an ionic compound is split into its constituent gaseous ions under standard conditions
Born Haber Cycle
An energy level diagram breaking down the formation of an ionic compound into a series of simpler steps
Enthalpy change of hydration
The enthalpy change when one mole of gaseous ions is surrounded by water molecules to form an infinitely dilute solution under standard conditions
