Energetics

An open system can exchange energy and matter with the surroundings. A closed system can exchange energy but not matter with the surroundings.

Temperature is the average kinetic energy of molecules (K, kelvins)

Heat is the amount of energy exchanged due to a temperature difference between two substances (J, joules)

Enthalpy is the amount of energy or heat content of a substance. The energy is stored in chemical bonds. It incudes kinetic and potential energy and is not measured directly but changers are measured (J)

The difference between the enthalpy of the products and of the reactants at 298K and 1.00 x 10^5Pa

Enthalpy of products - enthalpy of reactants

The higher the value of enthalpy, the less stable the substance

-Combustion reactions -Neutralization reactions

Q (J) = mass (g) x specific heat capacity(J g–1 K–1) x change in temp (K)

-100kPa -1 mol/dm3 for all solutions -all substances in there standard states

The standard state of a substance is the pure form of the substance under standard conditions of 298 K (25 °C) and 1.00 × 10^5 Pa

4.18 J g–1 K–1

The standard enthalpy change of combustion is the enthalpy change for the complete combustion of one mole of a substance in its standard state in excess oxygen under standard conditions

1 no heat loss from the system 2 all the heat goes from the reaction to the water 3 the solution is dilute: V(CuSO4) = V(H2O) 4 water has a density of 1.00 g cm–

The enthalpy change for any chemical reaction is independent of the route, provided the starting conditions and final conditions, and reactants and products, are the same.

The standard enthalpy of formation of a substance is the enthalpy change that occurs when one mole of the substance is formed from its elements in their standard states under standard conditions of 298 K (25 °C) and 1.00 ×10^5 Pa

∆H reaction =∑∆H⊖f (products) – ∑∆H⊖f (reactants

The average bond enthalpy is the energy needed to break one mole of bonds in gaseous molecules under standard conditions averaged over similar compounds.

The ionization energy is the minimum energy required to remove one mole of electrons from one mole of gaseous atoms.

Electron affinity is the enthalpy change when one mole of gaseous electrons is added to one mole of gaseous atoms

The lattice enthalpy is the enthalpy change that occurs when one mole of a solid ionic compound is separated into gaseous ions under standard conditions.

The enthalpy change of atomization is the enthalpy change that occurs when one mole of gaseous atoms is formed from the element in its standard state

The heat capacity (C) is defined as the heat needed to increase the Temperature of an object by 1 K

The specific heat capacity (c) is defined as the heat needed to increase the temperature of unit mass of material by 1 K