Download Unit 8-10 Review Answers

Unit 8, 9 and 10 Review
Concepts to know: (review the polyatomic ions)
Unit 8: balance chemical reactions
Identify reaction types (synthesis, decomposition, combustion, single and double replacement)
Predict products in a chemical reaction given the reactants
Unit 9: Stoichiometry
Percent yield
Limiting reactants
Unit 10: properties of gases
Properties of liquids- surface tension, volatility, capillary action
Properties of solids
Pressure (convert between units)
Convert from Celsius to Kelvin
Kinetic energy- proportional to temperature
Lighter molecules move faster than heavier ones at the same temperature
Phase changes (melting, freezing, boiling, condensation, sublimation, deposition)
Exothermic –heat is released, heat is a product, ∆H is negative, temp. increases
Endothermic-heat is absorbed, heat is a reactant, ∆H is positive, temp. decreases
Heating curves
Molar heats of vaporization and molar heats of fusion
Practice problems
1. Rank the following pressures in increasing order:
(a) 50 kPa
(b) 76 torr
(c) 2 atm
(d) 340 mmHg
b,d,a,c
2. List the following attractive forces in order of increasing strength: c, d, a, b
(a) hydrogen bonding
(b) ionic bonding (c) London dispersion forces
(d) dipole-dipole forces
3. All of the following statements about liquids and gases are true except .
(a) Molecules in a liquid are much more closely packed than molecules in a gas.
(b) Molecules in a liquid can vibrate and rotate, but they cannot move about freely as molecules in a gas.
(c) Liquids are much more difficult to compress into a smaller volume than are gases.
(d) Liquids diffuse more slowly than gases.
4. Experiments show that it takes 6.0 kJ of heat energy to melt 1 mol of ice at its melting point but only about 0.6 kJ to melt 1 mol of
methane, CH4, at its melting point. Explain in terms of intermolecular forces why it takes so much less energy to melt the methane.
Water has hydrogen bonds holding its molecules together and methane only has London dispersion which is much easier
to break so it doesn’t take as much energy to break them apart
5. The molar heat of vaporization of methane, CH4, is 8.19 kJ/mol; for water, it is 40.79 kJ/mol.
a. Based on the molar heat of vaporization data, which is more volatile, CH4 or H2O? CH4
b. Which molecule is more polar, CH4 or H2O? water
6. Finish balancing the following equation: 3Fe3O4 + __8_Al Al2O3 + ___9__Fe
7. In each of the following formulas with coefficients, write the total number of atoms present.
a. 4SO2
b. 8O2
c. 3Al2(SO4)3
12
16
27
8. Convert the following word equation into a balanced chemical equation:
aluminum metal + copper(II) fluoride aluminum fluoride + copper metal
2Al + 3CuF2  2AlF3 + 3Cu
9. Why do you think water vapor is less volatile than CCl4? Water has hydrogen bonding holding it together and CCl4 has only
London Dispersion forces. It is much harder to break hydrogen bonds and so it is harder to evaporate.
10. If the actual yield of a reaction is 22 g and the theoretical yield is 25 g, calculate the percent yield. 88%
11. 6.0 mol of N2 are mixed with 12.0 mol of H2 according to the following equation: N 2(g) + 3H2(g) 2NH3(g)
a. Which chemical is in excess? What is the excess amount in moles? Nitrogen, 2 mol
b. Theoretically, how many moles of NH3 will be produced? 8 moles
12. Compare a polar water molecule with a less-polar molecule, such as formaldehyde, CH2O. Both are liquids at room temperature
and 1 atm pressure.
a. Which liquid should have the higher boiling point? water b. Which liquid is more volatile? formaldehyde
c. Which liquid has a higher surface tension? water
d. Which liquid diffuses more rapidly? water
13. What happens to the kinetic energy when water boils? What happens to the temperature of the water when it boils?
Stays the same; stays the same
14. What happens to the potential energy when water boils? Explain.
Increases, energy put in to boil is used to break attractions
15. Why does a substance diffuse/effuse faster at higher temperatures? Molecules are moving faster
16. At 20 °C, which gas will diffuse the fastest, chlorine or nitrogen? Why? Nitrogen, smaller molecules move faster
17. At 50 °C, which gas has the highest kinetic energy, neon or argon? Same kinetic energy
18. H2O + 241.8 kJ  H2 + ½ O2
a. Is heat being taken in or released as liquid decomposes? Taken in
b. Will ∆H be positive or negative? Will the temperature increase or decrease as the reaction proceeds? Positive; decrease
19. Convert
a. -50° C to Kelvin
b. 0.50 atm to mmHg
c. 0 °C to Kelvin
223K
380 mmHg
273K
20. The combustion of C2H2 has a ∆H of -1301 kJ. Write a balanced equation for this and include heat in the reaction.
a. Will this feel hot or cold?
b. Is this exothermic or endothermic?
Hot
exothermic
21. label the following as exothermic or endothermic
a. melting
b. deposition
c. evaporation
d. freezing
endothermic
exothermic
endothermic
exothermic
22. Write a balanced reaction when chlorine reacts with sodium iodide and find the grams of sodium iodine that reacts with 2.40 g of
chlorine. Cl2 + 2NaI  2NaCl + I2
10.3 g
23. 2 KClO3 + heat  2 KCl + 3O2
a. How many moles of oxygen form as 3.0 mol of potassium chlorate are totally consumed? 4.5 mol
b. Is this reaction exothermic or endothermic endothermic
24. Which coefficients would you add to balance the chemical equation Fe + O 2 Fe2O3?
a. 2, 3, 1
b. 3, 2, 1
c. 4, 3, 2
d. The equation is already balanced.
25. Complete the chemical equation by writing in the products formed and balancing the final equation.
a. 3Ba(NO3)2(aq) + 2Na3PO4(aq) a3(PO4)2 + 6NaNO3
b. 4Al(s) + 3O2(g) l2O3
c. I2(s) + 2NaBr(aq) aI + Br2
d. 2C3H4(g) +5 O2(g) CO2 + 4H2O
e. decomposition of molten potassium chloride 2KCl  2K + Cl2
26. Match the equation type on the left to its representation on the right.
synthesis c
(a) AX + BY AY + BX
decomposition d
(b) A + BX AX + B
single replacement b
(c) A + B AX
double replacement a
(d) AX A + X
27. Of the following chemical equations, the only reaction that is both synthesis and
combustion is
(a) C(s) + O2(g) CO2(g)
(b) 2C4H10(l ) + 13O2(g) 8CO2(g) + 10H2O(l )
(c) 6CO2(g) + 6H2O(g) C6H12O6(aq) + 6O2(g)
(d) C6H12O6(aq) + 6O2(g) 6CO2(aq) + 6H2O(l )
28. The complete combustion of a hydrocarbon in excess oxygen yields the products __CO2_______and___H2O________
29. For the following four reactions, label the type, predict the products (make sure formulas are correct), and balance the equations:
a. Cl2(aq) + 2NaI(aq) aCl + I2; single replacement
b. 3Mg(s) + N2(g) g3N2; synthesis
c. Co(NO3)2(aq) + H2S(aq) CoS + 2HNO3; double replacement

30. Acetylene gas, C2H2, is burned to provide the high temperature needed in welding.
a. Write the balanced chemical equation for the combustion of C2H2 in oxygen. 2C2H2 + 5O2 4CO2 + 2H2O
b. If 1.0 mol of C2H2 is burned, how many moles of CO2 are formed? 2 moles
c. How many moles of oxygen gas are consumed? 2.5 moles