How do you write a chemical equation for a reaction?

To write a chemical equation for a reaction, you need to identify the reactants, products, and their respective quantities.

Writing a chemical equation involves several steps. First, you need to identify the reactants, which are the substances that react with each other. These are usually written on the left side of the equation. Next, you need to identify the products, which are the substances that are formed as a result of the reaction. These are written on the right side of the equation.

The reactants and products are represented by their chemical symbols or formulas. For example, in the reaction between hydrogen and oxygen to form water, the reactants are hydrogen (H2) and oxygen (O2), and the product is water (H2O). This would be written as H2 + O2 → H2O.

However, this equation is not balanced. A balanced chemical equation has the same number of each type of atom on both sides of the equation. In the above example, there are two oxygen atoms on the left side (in O2) but only one on the right side (in H2O). To balance the equation, we can adjust the quantities of the reactants and products. The balanced equation is 2H2 + O2 → 2H2O, which indicates that two molecules of hydrogen react with one molecule of oxygen to form two molecules of water.

In addition to balancing the atoms, you also need to indicate the physical state of each substance (solid, liquid, gas, or aqueous) using the symbols (s), (l), (g), and (aq) respectively. If heat or light is required for the reaction, this is indicated above the arrow. For example, the balanced equation for the combustion of methane in oxygen is CH4(g) + 2O2(g) → CO2(g) + 2H2O(l), ΔH = -890 kJ/mol, indicating that the reaction is exothermic (releases heat).

Remember, writing and balancing chemical equations is a fundamental skill in chemistry, as it allows you to predict the products of a reaction and calculate the quantities of reactants needed or products formed.