Balanced Equations
Why do we need to balance chemical equations?
To show mass is conserved.
Chemistry rearranges elements, it does not create or destroy matter.
What is the mole ratio between HCl and H2O?
HCl + KOH --> KCl + H2O
1 mole HCl = 1 mole H2O
How many moles of CuCl2 react to form 37 moles of NaCl?
CuCl2 + Na2SO4 -->CuSO4 + 2NaCl
37 mol NaCl * (1 mol CuCl2 / 2 mol NaCl) = 18.5 mol CuCl2
CH4 + 3 Cl2 --> CHCl3 + 3 HCl
6.72 g CH4 produces 50 g CHCl3
6.72 g Cl2 produces 3.8 g CHCl3
If you have 6.72 g of each reactant, which is the limiting reactant? Which is the excess reactant? How much CHCl3 can be made?
Limiting Reactant: Cl2
Excess Reactant: CH4
Product: 3.8 g, then the reaction stops
What is the formula for percent yield?
hint: % = part/whole *100%
(actual yield / theoretical yield) * 100%
Balance this equation:
__ Na + __ H2O --> __ NaOH + __ H2
2 Na + 2 H2O --> 2 NaOH + H2
If you have 25 moles of NH4NO3 and want to find moles of H2O, how would you setup the mole ratio?
NH4NO3 --> N2O + 2H2O
setup like a fraction:
TOP: 2 mole H2O
BOTTOM: 1 mol NH4NO3
Fe2O3 + 2Al --> 2Fe + Al2O3
What is the mass of Al that reacts with 5 moles of Fe2O3?
Make sure you've shown 2 steps:
269.8 g Al
2H2 + O2 --> 2H2O
You have 7 moles of H2 and 5 moles of O2. What is the limiting reactant?
Show moles H2 to moles H2O: 7 moles H2O
Show moles O2 to moles H2O: 10 moles H2O
H2 is limiting reactant
What is the theoretical yield of PbO if 200 g of PbS is reacted?
2PbS + 3O2 --> 2PbO + 2SO2
186.6 g PbO
Show (through math or reasoning) that mass is conserved in the following equation:
N2 + 3 H2 --> 2 NH3
2(14.01) + 6(1.01) = 2(14.01) + 6(1.01)
OR
two atoms of Nreactants = 2 atoms Nproducts
6 atoms of Hreactants = 6 atoms of Hproducts
What is the mole ratio of NaN3 to N2?
UNBALANCED equation:
NaN3 --> Na + N2
2NaN3 --> 2Na + 3N2
2 mol NaN3 = 3 mol N2
!!!!SURPRISE MS. JOHNSON QUESTION!!!!
What is Ms. Johnson's favorite flavor of ice cream?
Bonus point: What is her least favorite flavor of ice cream?
Worst ice cream ever: mint chocolate chip
get your toothpaste flavor out of my ice cream
CO + 2H2 --> CH3OH
If you are given 10 g CO and 15 g H2, what is the limiting reactant? What is the excess reactant?
CO makes .36 mol CH3OH
H2 makes 3.71 mol CH3OH
L.R. = CO
E.R. = H2
In lab, 200 g of PbS was reacted with excess oxygen. The researcher collected 170.0 g of PbO. What is the percent yield?
2PbS + 3O2 --> 2PbO + 2SO2
170/186.6*100= 91.1%
Balance this equation:
_Zn + _HNO3 --> _Zn(NO3)2 +_N2O + _H2O
4Zn + 10HNO3 --> 4Zn(NO3)2 + N2O + 5H2O
Write ALL the possible mole ratios:
TiO2 + C + 2Cl2 --> TiCl4 + CO2
1 mol TiO2 = 1 mol C
1 mol TiO2 = 2 mol Cl2
etc
... you should have 10 mole ratios listed
4KO2 + 2H2O +4CO2 --> KHCO3 + 3O2
If 380 g of O2 were produced form this reaction, what was the starting mass of KO2?
Make sure you have 3 steps shown
1100 g KO2
What is the mass of Zn(OH)2 produced when 25 g Zn reacts with 30 g MnO2?
2 separate math problems should show potential amount of Zn(OH)2 that could be made.
Answer: 17.1 g Zn
MnO2 + 4HCl --> MnCl2 + Cl2 + 2 H2O
A researcher collected 20 g of Cl2 from 86 g MnO2 and 50 g HCl. What is the percent yield
(hint: this question is really long)
theoretical yield: 24.3 g Cl2
percent yield: 20/24.3 *100 = 82.3%