A chemical reaction is a process in which one or more substances change into one or more new substances. This change is accompanied by the release or absorption of energy and the rearrangement of atoms.

The main types of chemical reactions are combination reactions, decomposition reactions, single-replacement reactions, double-replacement reactions, and combustion reactions.

The rate of a chemical reaction is affected by the concentration of reactants, temperature, surface area of reactants, and the presence of a catalyst.

A catalyst is a substance that speeds up a chemical reaction by providing an alternative pathway for the reaction to take place.

Chemical reactions are used in a wide variety of applications, including producing food, producing energy, producing medicines, and producing materials.

The chemical equation for the combustion of methane is $$CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O$$. This reaction is a combination reaction in which methane and oxygen react to form carbon dioxide and water.

The chemical equation for the decomposition of water is $$2H_2O \rightarrow 2H_2 + O_2$$. This reaction is a decomposition reaction in which water breaks down into hydrogen and oxygen.

The chemical equation for the single-replacement reaction between zinc and copper sulfate is $$Zn + CuSO_4 \rightarrow ZnSO_4 + Cu$$. In this reaction, zinc replaces copper in copper sulfate to form zinc sulfate and copper.

The chemical equation for the double-replacement reaction between sodium chloride and silver nitrate is $$NaCl + AgNO_3 \rightarrow NaNO_3 + AgCl$$. In this reaction, the cations of sodium and silver switch places to form sodium nitrate and silver chloride.

The chemical equation for the combustion of propane is $$C_3H_8 + 5O_2 \rightarrow 3CO_2 + 4H_2O$$. This reaction is a combustion reaction in which propane reacts with oxygen to form carbon dioxide and water.

The chemical equation for the decomposition of hydrogen peroxide is $$2H_2O_2 \rightarrow 2H_2O + O_2$$. This reaction is a decomposition reaction in which hydrogen peroxide breaks down into water and oxygen.

The chemical equation for the single-replacement reaction between magnesium and hydrochloric acid is $$Mg + HCl \rightarrow MgCl_2 + H_2$$. In this reaction, magnesium replaces hydrogen in hydrochloric acid to form magnesium chloride and hydrogen.

The chemical equation for the double-replacement reaction between sodium hydroxide and sulfuric acid is $$NaOH + H_2SO_4 \rightarrow Na_2SO_4 + H_2O$$. In this reaction, the cations of sodium and hydrogen switch places to form sodium sulfate and water.

The chemical equation for the combustion of ethanol is $$C_2H_5OH + 3O_2 \rightarrow 2CO_2 + 3H_2O$$. This reaction is a combustion reaction in which ethanol reacts with oxygen to form carbon dioxide and water.