​Evidence for a Chemical Reaction

• ​color changes

• a solid forms (precipitate)

• bubbles form

• heat or a flame is produced

• heat is absorbed (becomes cold)

​Chemical Equation

​Chemical Reaction -- the rearrangement of the ways in which atoms are grouped.

Chemical Equation -- A representation of a chemical reaction showing the relative numbers of reactant and product molecules.

​Reactants -- chemicals present before the reaction and are shown to the left of the arrow.

Products -- chemicals present after the reaction and are shown to the right of the arrow.

​Conservation or Matter

​In a chemical reaction, atoms are neither created nor destroyed.

All atoms present in the reactants must be accounted for among products

​Subscripts

A subscript is a small number written at the bottom of the symbol. If the number is on the right side, it depicts the number of atoms of the element present in the molecule.

​Counting Atoms

​Subscripts tells us how many atoms of a certain element are in a chemical equaiton.

• ​Coefficients are used to balance chemical equations.

• The smallest integers (whole numbers) are used to balance the equations.

• The coefficient must go in front of the chemical formula.

• The number 1 is never used as a coefficient.

​Coefficients

​Coefficients are used to balance chemical equations. The coefficient multiplies everything in the chemical formula.

In the equation above, there are 4 hydrogen and 2 oxygen to the left of the arrow and 4 hydrogen and 2 oxygen to the right of the arrow.

​ 4 = H = 4

2 = O = 2

​How to Balance a Chemical Equation.