1. Chemical Changes

2. A. Describing chemical reactions-a change of one or more substances converted into new substances. 1. Reactants are substances that combine or change (charcoal-coal) 2. New substances that are produced are called products.

3. 1. Antoine Lavoisier experimented with mercury (II) oxide and heat 2. He found the mass of products (liquid mercury and oxygen gas) equaled the mass of the reactants.

4. 1. Chemical formula expresses relationship between element in the compound and molecules they make up 2. Coefficients are numbers representing the number of units of each substance in a reaction.

5. 3. Knowing coefficients of chemical reactions allows chemists to use the correct amounts of reactants to predict the amounts of products. 4. Subscripts are numbers representing the number of atoms in a molecule of a particular element. 5. Symbols are used to show the state of the reactant: (s) solid, (aq) aqueous, (g) gas, (l) liquid.

6. React with the atmosphere in different ways.

7. Answer: Chemists need to know how much of a reactant will produce a certain amount of a product.

8.  http://education.jlab.org/elementbalancing/ question.php?4527451 http://education.jlab.org/elementbalancing/ question.php?4527451