rate of reaction - answer-the change in concentration of a reactant or product per unit time rate constant (k) - answer-The constant that links the rate of reaction with the concentrations of the reactants raised to the powers of their orders in the rate equation. half-life - answer-The time taken for the concentration of the reactant to reduce by half Benzene - answer-a naturally occurring aromatic compound, which is a very stable planar ring structure with delocalised electrons Model - answer-a simplified version that allows us to make predictions and understand observations more easily Lattice enthalpy - answer-The enthalpy change that accompanies the formation of one mole of an ionic lattice from its gaseous ions under standard conditions e.g. K+(g) + Cl-(g) -> KCl(s) - enthalpy change standard enthalpy chang