How to Balance Chemistry Equations
Question
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How to Balance Chemistry Equations

A chemical equation describes what happens in a chemical reaction. The equation identifies the reactants and products, the formulas of the participants, the phases of the participants such as solid, liquid and gas, and the amount of each substance. Balancing a chemical equation refers to establishing the mathematical relationship between the quantity of reactants and products. The quantities are expressed as grams or moles.
Steps to Balancing a Chemistry Equation

There are essentially three steps to the process:
Write the unbalanced equation
Balance the equation
Indicate the states of matter of the reactants and products
Tin oxide is heated with hydrogen gas to form tin metal and water vapor.
Write the Unbalanced Chemistry Equation

In the first step, write the unbalanced equation.

SnO2 + H2 → Sn + H2O
Balance the Chemistry Equation

The second step is to balance the equation.

Look at the equation and see which elements are not balanced. In this case, there are two oxygen atoms on the left hand side of the equation and only one on the right hand side. Correct this by putting a coefficient of 2 in front of water:

SnO2 + H2 → Sn + 2 H2O

This puts the hydrogen atoms out of balance. Now there are two hydrogen atoms on the left and four hydrogen atoms on the right. To get four hydrogen atoms on the right, add a coefficient of 2 for the hydrogen gas. Remember, coefficients are multipliers, so if we write 2 H2O it denotes 2x2=4 hydrogen atoms and 2x1=2 oxygen atoms.

SnO2 + 2 H2 → Sn + 2 H2O

The equation is now balanced.
Indicate the States of Matter

In the third and final state, indicate the physical states of the reactants and products. Oxides are solids, hydrogen forms a diatomic gas, tin is a solid, and the term 'water vapor' indicates that water is in the gas phase:

SnO2(s) + 2 H2(g) → Sn(s) + 2 H2O(g)

This is the balanced equation for the reaction.