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Name_______________________________________________period________Chapter 5 worksheet
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What is energy? The measure of the ability to do work
What is heat? A form of energy that is transferred because of temperature differences
What is the SI unit for heat? Joule
What is an exothermic reaction? A reaction where energy is released
What is an endothermic reaction? A reaction where energy is absorbed
What is enthalpy? The heat content of a substance
What is the sign of ΔH for an exothermic reaction? negative
What is the sign of ΔH for an endothermic reaction? positive
Consider the following reaction, which occurs at room temperature and pressure:
2Cl (g)  Cl2 (g)
ΔH = -243.4 kJ
Which has higher enthalpy under these conditions, 2Cl (g) or Cl2(g)
10. Consider the following reaction:
2Mg(s) + O2(g)  2MgO(s)
ΔH = -1204 kJ
a. Is this reaction exothermic or endothermic? exothermic
b. Calculate the amount of heat transferred when 2.4 g of Mg react 59 J released
c. Will the surroundings get warmer or colder when the reaction proceeds? Warmer
11. How much heat is released when 15.0 g of copper with a specific heat capacity of 0.385 J g-1⁰C-1 is cooled from
80 ⁰C to 35 ⁰C?
260 J
12. If 500 J of heat are added to 100.g sample of each of the substances listed below, which will have the largest
temperature increase?
Gold specific heat = 0.129 J g-1K-1
Silver specific heat = 0.237 J g-1K-1
Copper specific heat = 0.385 J g-1K-1
Water specific heat = 4.18 J g-1K-1
13. If 100.0 J of heat are added to a 150.0 g sample of water at 25.0 ⁰C, what is the final temperature of the water?
25.159 ⁰C
14. What are more thermodynamically favored, exothermic or endothermic reactions?
exothermic
15. Will exothermic reactions feel hot or cold?
hot
16. Will endothermic reactions feel hot or cold?
cold
17. The heat released from the combustion of 0.0500 g of white phosphorus increases the temperature of 150.0 g of
water from 25.0 ⁰C to 31.5 ⁰C. Calculate the value of the enthalpy change in kJ mol-1 of the combustion of
phosphorus.
-4500 kJ mol-1
18. When a 6.50 g sample of solid sodium hydroxide dissolves in 100.0 g of water in a Styrofoam cup, the
temperature rises from 21.6 ⁰C to 37.8 ⁰C. Calculate ΔH (in kJ mol-1) for the solution process.
-42.3 kJ mol-1
19. Consider the combustion of liquid methanol:
CH3OH (l) + 3/2 O2(g)  CO2 (g) + 2H2O (l)
ΔH = -726.5 kJ
a. What is the enthalpy change for the reverse reaction?
726.5 kJ
b. Balance the forward reaction with whole-number coefficients. What is ΔH for the reaction
represented by this equation?
2CH3OH (l) + 3 O2(g)  2CO2 (g) + 4H2O (l)
ΔH = -1453kJ
c. Which is more likely to be thermodynamically favored the forward or reverse reaction?
forward
d. If the reaction were written to produce H2O (g) instead of H2O (l), would you expect the magnitude
of ΔH to increase, decrease, or stay the same? Explain.
It takes energy to go from liquid water to gaseous water, so ΔH would increase (less negative)
20. Given the following enthalpies of reaction:
P4(s) + 3O2(g)  P4O6 (s)
ΔH = -1640.1
P4(s) + 5O2(g)  P4O10(s)
ΔH = -2940.1
Calculate the enthalpy change for P4O6(s) + 2O2(g)  P4O10(s)
-1300 kJ
21. Given the following enthalpies of reaction:
H2(g) + F2(g)  2HF(g)
ΔH = -537kJ
C(s) + 2F2(g)  CF4(g)
ΔH= -680 kJ
2C(s) + 2H2(g)  C2H4(g)
ΔH=52.3 kJ
Calculate the enthalpy change for C2H4 (g) + 6F2(g)  2CF4(g) + 4HF(g)
-338 kJ
22. What is meant by standard conditions with reference to enthalpy changes?
Room temperature and all compounds/elements are in their standard states
23. Which of the following does not have a standard heat of formation value of zero at 25 ⁰C and 1.00 atm?
a. Cl2(g)
b. I2 (s)
c. Br2(g)
d. Na(s)
24. Calculate the enthalpy change for the reactions
a.Fe3O4 (s) + 2C(s)  3Fe(s) + 2CO2 (g)
906 kJ
b.2NO2(g)  N2O4 (g)
-57.2 kJ
c. 4FeO(s) + O2 (g)  2Fe2O3(s)
-1100 kJ
Given the following ΔHf
Fe3O4 (s)
-118 kJ mol-1
CO2 (g)
-394 kJ mol-1
NO2(g)
33.2 kJ mol-1
N2O4 (g)
9.2 kJ mol-1
FeO(s)
-271.9 kJ mol-1
Fe2O3(s)
-822.16 mol-1
25. Is breaking bonds endothermic or exothermic?
endothermic
26. Is forming bonds endothermic or exothermic?
exothermic
27. Using bond energies from the data booklet, find the enthalpy change for the following reactions.
a. C2H4 + H2  C2H6
-124 kJ
b. 2H2 + O2  2H2O
-484 kJ
Try the practice questions on pg. 113
Review:
1. The density of aluminum is 2.7 g/mL. What is the volume of 8.1 g?
3.0 L
2. Na, K, Li, and Cs all share similar chemical properties. In the periodic table, they most likely belong to the
same
a. Row
b. period
c. group
d. element
3. An unknown element is shiny and a good conductor of electricity. What other properties would you predict
for it?
Malleable, ductile, high melting point/boiling points
4. Write the names of each element and identify them as a metal, nonmetal, metalloid, or noble gas
a. K
b. Si
c. Hg
d. Ag
e. Na
f. He
Potassium silicon
mercury
silver
sodium
helium
Metal
metalloid metal
metal
metal
noble gas
5. A certain ion has an atomic number of 16, a mass number of 33, and 18 electrons.
a. What is the charge on the ion? -2
b. What is the identity of this ion? sulfur
c. How many neutrons does the nucleus of this ion have? 17
6. What is the charge on a magnesium ion that has 10 electrons? +2
7. Find the mass for each of the following
a. 6.75 mol lead
b. 3.01 x 10 23 atoms of F
8. Find the number of atoms in each of the following (show work)
a. 1.50 mol Na
d. 0.025 kg aluminum
9. Find the number of moles in each of the following (show work)
a. 0.11 kg Na
d. 2.25 x 10 25 atoms Zn
10. For each group, tell if the atoms will gain or lose electrons to become ions and tell how many electrons are
involved.
a. Group 1
b. group 13
c. group 2
d. group 17
Lose 1
lose 3
lose 2
gain 1
11. Label each as forming ionic, covalent, or metallic bonds
a. AlN
b. CO2
c. Al foil
d. H2O
e. SnO
d. CuF2
Ionic
covalent
metallic
covalent
ionic
ionic
12. What is the formula when the following ions bond
a. Magnesium and fluoride MgF2
b. Magnesium and oxide MgO
c. Aluminum and bromide AlBr3
d. Sodium and oxide Na2O
e. Barium and hydroxide Ba(OH)2
13. Which of the following would have the highest boiling point and why? H2O or H2S
Water has hydrogen bonding holding the molecules together. Hydrogen sulfide has dipole-dipole which are not
as strong
14. What kind of attractive forces must be overcome to
a. Boil water
b. Melt KCl
c. Sublime(solid to gas) I2
d.Boil H2S
Hydrogen bonding
ionic
London dispersion(van der waals)
dipole-dipole
15. Nitrogen and carbon monoxide have almost equal masses. Explain why the boiling point of carbon monoxide is
slightly higher than that of nitrogen
It is polar so it has dipole-dipole forces where nitrogen only has London dispersion which is weaker.