physical change
any change that alters the form or appearance of a substance but does not change into another substance
chemical change
a change in which one or more substances combine or break apart to form new substances
reactants
substances that undergo chemical changes
products
the new substances that form
exothermic reactions
a reaction that usually releases energy, usually in the form of heat
endothermic reaction
a reaction that absorbs energy
chemical equation
a way to show a chemical reaction, using symbols instead of words
law of conservation of mass
the principle that the total amount of matter is neither created nor destroyed during any chemical of physical change
coefficient
a number placed in front of a chemical formula in an equation
activation energy
the minimum amount of energy needed to start a chemical reaction
catalyst
a material that increases the rate of a reaction by lowering the activation energy
inhibitor
a material that decreases the rate of a reaction