C HAPTER 8: C HEMICAL E QUATIONS & R EACTIONS By: Jessica Alphonse

C HEMICAL C HANGE A chemical reaction is a process in which one or more substance turns into a new substance. Some examples of chemical reactions include wood burning which turns into ash, metal rusting, and baking a cake. Signs of a chemical reaction include: color change odor given off Substance difficult to reverse. Gas released Solid forming into a liquid.

P HYSICAL C HANGE A physical change is a process in which the molecules of a substance have not change. Some examples of physical change include water melting, evaporating or freezing, concrete hardening, and different color paint mixing together. Signs of a physical change include making a mixture cutting dissolving Grinding Original properties are kept. Change of state.

B ALANCING C HEMICAL E QUATIONS Chemical equations show the amount of reactants & products. For a reaction to take place, molecules and atoms of the reactants must go together. In order to construct a chemical reaction, you must first write a word equation. Ex. Methane + Oxygen -  Carbon Dioxide. Use the arrow to separate the reactants and the products. Then turn them into a formula equation. Ex. ?CH4+ O2 -  ?CO2 + ?H2O.

T YPES OF R EACTIONS There are many different types of reactions you can easily identify what products are formed. Decomposition - one substance breaking up into 2 or more substances. Ex. 2H2O  2H2+O2 Synthesis- A combustion of 2 substances forming one substance. Ex. N2 + 4H2  2NH4 Combustion- a reaction in which a hydrocarbon reacts with oxygen to give CO2 + H2O. Displacement- A process in which a metal replaces another metal in an ionic compound. Ex. Zn+ CuSO4  ZnSO4+ Cu. Double Displacement- Metal ions forming 2 ionic compounds exchange positions. Ex. ZnPO4 + CuSO4  ZnSO4 + CuPO4

N ET I ONIC EQUATIONS An ionic compound can dissolve in water, which makes the ions separate and prove that the formula are aqueous ions. When 2 solutions combined, the ions also combine an react. Some ions do not react called spectator ions that remained unchanged. To write a net ionic equation, you need to write a balanced equation first. Then use a type of reaction to predict the products. After that, write the separate aqueous ions for each aqueous ionic substance. Then cancel the spectator ions and whatever remains is the net ionic equation.