Question | Answer |
chemistry | the study of the properties of matter and how matter changes |
element | a substance that cannot be broken down into any other substances by chemical or physical means |
compounds | a substance made of two or more elements chemically combined in a specific ratio |
mixture | made from two or more pure substances that are in the same place but not combined as a new material |
pure substances | element and compounds |
solution | a well-mixed mixture |
physical change | a change that alters the form or appearance of a material but does not make the material into another substance |
chemical change | a change in matter that produces new substances |
precipitate | a solid that forms from solution during a chemical reaction |
atom | the smallest particle of an element |
molecule | the combination of two or more atoms |
chemical bond | the force that holds atoms together |
chemical equation | a shorter, easier way to show chemical reactions, using symbols instead of words |
chemical formula | an element's one-letter or two-letter symbol |
subscript | a number written lower and smaller than the symbol of an element; shows the number of atoms of an element in a molecule |
reactants | the materials at the beginning of a chemical reaction |
principle of conservation of mass | the amount of matter in a chemical reaction does not change, so the total mass of the reactants must equal the total mass of the products |
coefficient | a number in front of a chemical formula that tells how many molecules or atoms of each reactant take part in the reaction |
synthesis | two or more substances combine to make a more complex compound |
decomposition | breaks down compounds into simpler products |
replacement reaction | one element replaces another in a compound or two elements in separate compounds trade places |
exothermic reaction | a chemical reaction that releases energy in the form of heat |
endothermic reaction | a chemical reaction that absorbs energy |
activation energy | the minimum amount of energy that has to be added to start a reaction |
concentration | the amount of material in a certain volume |
surface area | the amount of exposed material |
catalyst | a material that increases the rate of a reaction by lowering the activation energy |
enzymes | biological catalysts that provide a surface on which reactions take place |
inhibitor | decrease the rate of a chemical reaction by raising the activation energy, making it harder to get the reactions going |
combustion | a rapid reaction between oxygen and a substance called a fuel |
fuel | a material that releases energy when it burns |
fire triangle | 3 things necessary to start and maintain a fire: fuel, oxygen, and heat |