chapter 8. chemical change – a change in which the original substance(s) become something...
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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 productsTRANSCRIPT
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
4
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)