Definition of dray. : a vehicle used to haul goods; especially : a strong cart or wagon without sides.
The main difference between an equation and a function is the fact that an equation usually deals with a single input, whereas, a function can have numerous inputs. In mathematics, an equation is used to denote the equality between two expressions.
A word equation represents the ingredients of the reaction. The reactants and products are written in words. The '+' symbol shows the separate ingredients, while the ' ' symbol stands for 'reacts to form'. Chemical equations go a bit further by being more specific about the formulae involved.