chapter 8. chemical change – a change in which the original substance(s) become something...

Chapter 8

• chemical change – a change in which the original substance(s) become something different with completely different properties• indicated by:

• production of heat, light or electricity• formation of a precipitate or a gas• possible color change• new substance(s), products, have different

properties than original substance(s), reactants

• chemical equation – a shorthand method of showing what is happening in a chemical Rx• similar to a recipe

• shows what needs to be mixed and what will be made

• shows how much needs to be mixed and how much will be made

• shows the phases of the reactants and products

steps to balance a chemical equation1. start with a word equation

propane(C3H8) gas burns in the presence of oxygen in the air to form carbon dioxide gas and water vapor

2. create a skeletal equation• convert chemical names to chemical

symbols

C3H8(g) + O(g) CO2(g) + H2O(g)

3. create formula equation• check each formula• molecules –> from name• salts –> oxidation = reduction• diatomic elements

C3H8(g) + O (g) CO2(g) + H2O(g)

• once all formulas are correct, NEVER CHANGE OR ADD SUBSCRIPTS!!!!!!!• #1 mistake = incorrect formulas

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4. balance by inspection• count atoms/ions on reactant side• count atoms/ions on product side• FOLLOW LAW OF CONSERVATION OF

MASS – what you start with you must end with!!!!

C3H8(g) + O2 (g) CO2(g) + H2O(g)

3 C as a reactant, add a coefficient of 3 in front of C as a product

C3H8(g) + O2 (g) CO2(g) + H2O(g)3

C3H8(g) + O2 (g) 3CO2(g) + H2O(g)

8 H as reactant, add a 4 as a coefficient in front of H on product side

C3H8(g) + O2 (g) 3CO2(g) + H2O(g)

C and H are balanced, count O as reactant and O as product

2 O as reactant, 10 as product

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C3H8(g) + O2 (g) 3CO2(g) + 4H2O(g)

add a coefficient of 5 to the reactant O2

C3H8(g) + O2 (g) 3CO2(g) + 4H2O(g)

5. recheck all atoms/ions• start with first reactant

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• a sulfuric acid(H2SO4) solution is added to an aqueous solution of sodium hydroxide which forms an aqueous solution of sodium sulfate and water

• solid potassium chlorate when mixed with a catalyst of manganese dioxide will decompose in to solid potassium chloride and oxygen gas

• a solid piece of copper is added to an aqueous solution of silver nitrate which creates solid silver and a copper(II) nitrate solution

• an aqueous solution of barium nitrate is added to an aqueous solution of aluminum sulfate to produce an aqueous solution of aluminum nitrate and a precipitate of barium sulfate

Types of chemical Rx1. synthesis Rx• simple reactant + simple reactant

single product• A + X AX• example

2. decomposition Rx• single reactant two or more products• AX A + X• ABX AB + X

• types of decomp Rx

• example

3. single displacement Rx• element + compound different

element + different compound• AX + B BX + A

• example

4. double displacement Rx• compound + compound different

compound + different compound• one must be: a solid precipitate, or a gas,

or water.• AX + BY AY + BX(s),(g),(l)

• example

5. combustion Rx• hydrocarbon + oxygen carbon dioxide

+ water• three things needed for combustion• 1. fuel(hydrocarbon)• 2. oxygen• 3. NRG source to ignite

• products of complete hydrocarbon combustion are always• 1. carbon dioxide gas• 2. water vapor

• example

ionic equation all aqueous substances break apart in to ions NaCl(aq) Na+(aq) + Cl-(aq)

NaCl(aq) + AgNO3(aq) NaNO3 (aq) + AgCl(s)

Na+(aq) + Cl-(aq) + Ag+(aq) + NO3-(aq)

Na+(aq) + NO3-(aq) + AgCl(s)

net ionic equation list only ions reacting and what they make deduct/eliminate the spectator ions

spectator ions – ions that remain the same on both reactant and product side

Na+(aq) + Cl-(aq) + Ag+(aq) + NO3-(aq)

Na+(aq) + NO3-(aq) + AgCl(s)

Cl-(aq) + Ag+(aq) AgCl(s)