Chemical Chemical EquationsEquations

Chemical change involves a Chemical change involves a reorganization of the atoms in reorganization of the atoms in

one or more substances.one or more substances.

Chemical EquationChemical Equation

A representation of a chemical A representation of a chemical reaction:reaction:

CHCH44 + O + O22 COCO22 + H + H22OO reactantsreactants productsproducts

Physical StatesPhysical States

When you see a chemical formula, often When you see a chemical formula, often the formula is followed by a symbol in the formula is followed by a symbol in parentheses. For example:parentheses. For example:

HH22O(l) - the water is liquidO(l) - the water is liquid HH22O(s) - the water is solid (ice)O(s) - the water is solid (ice) HH22O(g)- the water is a gas (steam)O(g)- the water is a gas (steam) NaCl(aq) – means that the chemical is NaCl(aq) – means that the chemical is

disolved in water. In this case it would disolved in water. In this case it would be salt dissolved in water. be salt dissolved in water.

The Magnificent 7The Magnificent 7(diatomic molecules)(diatomic molecules)

Certain elements do not exist Certain elements do not exist naturally as a single atom. They exist naturally as a single atom. They exist in pairs. in pairs.

So when writing out a chemical So when writing out a chemical equation it is important to write the equation it is important to write the chemical formula to show that.chemical formula to show that.

The 7 are: HThe 7 are: H22, N, N22, O, O22, F, F22, Cl, Cl22, Br, Br22, and , and II22

Types of ReactionsTypes of Reactions

Synthesis ReactionSynthesis Reaction When two or more reactants come together When two or more reactants come together

to make one product. Also called to make one product. Also called Combination.Combination.

Example:Example:N2 + H2 NH3

Note that diatomic molecules (Magnificent 7!) must be diatomic in their elemental form.

Decomposition ReactionDecomposition Reaction When a single compound is broken When a single compound is broken

down into two or more productsdown into two or more products

Example:Example:H2O H2 + O2

Single Displacement ReactionSingle Displacement Reaction When an element and an ionic When an element and an ionic

compound react and the element compound react and the element takes the place of its comparable ion takes the place of its comparable ion Metal element Metal element takes positive ion’s place takes positive ion’s place Nonmetal element Nonmetal element takes negative ion’ takes negative ion’

placeplace Examples:Examples:

Mg + FeCl3 MgCl2 + FeBr2 + FeCl3 FeBr3 + Cl2

Mg + FeCl3 MgCl2 + FeBr2 + FeCl3 FeBr3 + Cl2

Notice!Notice! The neutral atom joins the compound The neutral atom joins the compound

becoming a charged ion. becoming a charged ion. The products MUST be electronically The products MUST be electronically

neutral. Since Mg becomes Mgneutral. Since Mg becomes Mg+2,+2, two Cl two Cl ions neutralize it.ions neutralize it.

The charge on the transition metal stays The charge on the transition metal stays the same if it remains as an ion (iron is +3 the same if it remains as an ion (iron is +3 charge in both the reactant and product)charge in both the reactant and product)

Double Displacement ReactionDouble Displacement Reaction When two ionic compounds switch their When two ionic compounds switch their

partner ions. partner ions. Positive goes with other negative and vice Positive goes with other negative and vice

versa. versa. Switcheroo!Switcheroo!

Example:Example:NaCl + MgBr2 MgCl2 + NaBrPb(NO3)2 + Na2SO4 NaNO3 + PbSO4

NaCl + MgBr2 MgCl2 + NaBrPb(NO3)2 + Na2SO4 NaNO3 + PbSO4

Notice!Notice! The reactants and products MUST be The reactants and products MUST be

electronically neutralelectronically neutral All ions keep their charge from reactants to All ions keep their charge from reactants to

productsproducts Do not get fooled into thinking that if there Do not get fooled into thinking that if there

are a certain number atoms of an element are a certain number atoms of an element in the reactants, there will be the same in the reactants, there will be the same number in the products! number in the products!

Polyatomic ions are very common in these Polyatomic ions are very common in these types of reactions. Make sure you can spot types of reactions. Make sure you can spot them!them!

Combustion ReactionsCombustion Reactions When a hydrocarbon (something with When a hydrocarbon (something with

C’s and H’s and sometimes O’s – C’s and H’s and sometimes O’s – organic molecule) reacts with Oxygen organic molecule) reacts with Oxygen to form water and carbon dioxide and to form water and carbon dioxide and heat energy. heat energy.

Example:Example:CH4 + O2 CO2 + H2OC4H8 + O2 CO2 + H2O

Acid/Base reactionAcid/Base reaction When an acid reacts with a base, When an acid reacts with a base,

water formswater forms Acids produce HAcids produce H+ + in waterin water Bases produce OHBases produce OH- - in waterin water

Example:Example:HNOHNO33 + KOH + KOH HOH (or H HOH (or H22O) + KNOO) + KNO33

What type of equation are each of What type of equation are each of the following reactions?the following reactions?

P + O2 P2O5 C3H5O + O2 CO2 + H2ONH4NO3 N2O + H2O Fe2O3 + C Fe + COCO2 + H2O H2CO3

CuNO3 + Na2SO4 Cu2SO4 + NaNO3

Check Your AnswersCheck Your Answers P + O2 P2O5 Synthesis

C3H5O + O2 CO2 + H2O Combustion

NH4NO3 N2O + H2O Decomposition

Fe2O3 + C Fe + CO Single Displacement

Check Your AnswersCheck Your Answers

CO2 + H2O H2CO3 Synthesis

CuNO3 + Na2SO4 Cu2SO4 + NaNO3

Double Displacement