reactions and stoichiometry chapters 11-12. reactions reactants products
TRANSCRIPT
Reactions and Stoichiometry
Chapters 11-12
Reactions
Reactants Products
Balancing Reactions
Reactions must maintain conservation of mass, charge, and energy
Reactants and Products must have the same number of atoms of each element2H2 + O2 2H2O
Balancing Reactions
Reactions must maintain conservation of mass, charge, and energy
Reactants must have the same total charge as ProductsCu+1 + Fe+3 Cu+2 + Fe+2
Balancing Reactions
To balance a reaction:Do NOT change chemistry
(compounds, subscripts)Only change coefficients (big numbers
in front of chemicals)Coefficients can only be whole
numbers2H2 + O2 2H2O
Balancing Reactions
4Na + O2 2Na2O
2Al + 3Br2 2AlBr3
4Ni + 3O2 2Ni2O3
2HNO3 + Ca(OH)2 Ca(NO3)2 + 2H2O
Reaction Types
Synthesis Decomposition Single Replacement Double Replacement Combustion
Synthesis
Chemical change in which two or more substances react to form a single new substance (1 product)
Also called Combination
2Mg + O2 2MgO
Decomposition
Chemical change in which a single compound breaks down into two or more simpler products1 reactant
NaHCO3 NaOH + CO2
Single Replacement
Chemical change in which one element replaces a second element in a compoundMetal replaces metal (hydrogen included)
Nonmetal replaces nonmetal
Zn + 2HCl ZnCl2 + H2
Double Replacement
Chemical change involving an exchange of positive ions between compounds
AgNO3 + NaCl NaNO3 + AgCl
Combustion
Chemical change in which an element or a compound reacts with oxygen, often producing energy in the form of heat and light
2Mg + O2 2MgO
Combustion
Complete combustion of a hydrocarbon produces carbon dioxide and water
2C2H6 + 7O2 4CO2 + 6H2O
Spontaneous Reactions
A single replacement reaction will only occur if:The single element in the reactants is
more active than the element it replaces in the compound
Table J
The more active element:Does not want to be
aloneWants to be
combined with someone else
Spontaneous or not?
ZnCO3 + Mg MgCO3 + Zn
PbSO4 + Mn MnSO4 + Pb
3KNO3 + Al Al(NO3)3 + 3K
2HCl + Zn ZnCl2 + H2
2NaBr + I2 2NaI + Br2
YES
NO
YES
YES
NO
Spontaneous Reactions
A double replacement reaction will only occur if:A precipitate (solid) is producedA liquid is produced
• H2O(l)
A gas is produced
Table F
Spontaneous or not?
NaCl + AgNO3 NaNO3 + AgCl
K2CO3 + MgSO4 K2SO4 + MgCO3
NH4OH + NaNO3 NaOH + NH4NO3
Yes
Yes
No
Stoichiometry
GoalThe role of coefficients in balanced
formula equations• Mole ratios in a balanced formula• Mole-mole stoichiometry problems
Stoichiometry
Calculations of quantities in chemical reactions
Food Example
How many pancakes can be made with 8 cups flour, excess eggs and milk?
pancakescupmilkeggscupsflour 10124
ratio 4 2 1 10
8 Xamount
X = 20 pancakes
Process for Solving
Balance reaction Copy coefficients from reaction into
ratio row Place numbers from question in row
above ratio row (Setting up proportion)
Solve for X using a proportion
Food Example
How many eggs are needed to make 25 pancakes?
pancakescupmilkeggscupsflour 10124
ratio 4 2 1 10
25Xamount
X = 5 eggs
Chemical Example
How many moles of NH3 can be made with 6 moles H2 and excess N2?
322 23 NHHN
ratio 1 3 2
6 Xamount
X = 4 mol NH3
=
Chemical Example
How many moles of N2 are needed to produce 7 moles of NH3?
322 23 NHHN
ratio 1 3 2
7Xamount
X = 3.5 mol N2
Chemical Example
How many moles of O2 are needed to produce 9 moles of H2O?
OHCOOHC 22283 435
ratio 1 5 3
9Xamount
X = 11.25 mol O2
4
Endo/Exothermic
Endothermic – Energy is absorbedEnergy term is on the left side
Exothermic – Energy is releasedEnergy term is on the right side
Treat just like a coefficient
Example
kJNHHN 8.9123 322
How much energy is produced when 6 moles H2 reacts with excess N2?
ratio 1 3 2
6 Xamount
91.8
X =183.6 kJ