Chemistry Test Review 1. In a chemical reaction, bonds are formed and broken. The breaking of bonds explains why certain reactions are exothermic and others are endothermic. Using enthalpy diagrams explain this statement. (4) Exothermic
Endothermic
2. Several factors affect the rate of chemical reactions. Two such factors are concentration and temperature. Using collision and activation energy theories to explain how concentration and temperature affect rate. Include kinetic energy diagrams with activation energy in your answer when appropriate. (6)
3. A sample of water with a mass of 210.5g undergoes a temperature change from 40.83°C to 98.73°C. What is the heat change in kilojoules? (2)
4. Calculate for ΔH for the reaction: (5)
HCl(g)
+
NaNO2(s)
→
HNO2(l)
+
2 NaCl(s) + H2O(l) → 2 HCl(g) + Na2O
ΔH = 507 kJ
NO(g) + NO2(g) + Na2O(s) → 2 NaNO2
ΔH = -427 kJ
NO(g) + NO2(g) → N2O(g) + O2(g)
ΔH = -43 kJ
2 HNO2(l) → N2O(g) + O2(g) + H2O(l)
ΔH = 34 kJ
NaCl(s)
5. When 1.75g of CaCl2 dissolves in 125g of water in a nested cup calorimeter, the temperature increased by 2.44°C. What is the heat change per mole of CaCl2 dissolved? Assume that the water absorbs all the heat. (3)
6. Define activation energy (2)
7. 5.50g of sodium hydroxide is dissolved in 175mL of water. Using a nested cup calorimeter, the temperature change of the water is measured to be 2.10°C. Write the thermochemical equation for this process. (3)
8. Use bond energies to estimate the heat of reaction, ΔH°, for: (4) CH4(g)
+
2 Cl2(g)
→
CH2Cl2(g)
+
2 HCl (g)
9. The following data were obtained for the reaction A + B → C + D, at 55°C
INITIAL [A] (mol/L)
INITIAL [B] (mol/L)
Initial Rate of Formation of C
0.100
0.100 1.00 x 103−
0.200
0.100 8.00 x 103−
0.300
0.100 2.70 x 102−
0.100
0.300 9.00 x 103−
a) Determine the rate law expression for this reaction. Show all calculations. (4)
b) Determine the rate law constant for this reaction. Remember to include units. (3)
c) Determine the initial rate of reaction if the [A]=[B]=0.400 mol/L (2)
10. When 0.150g of liquid octane, C8H18 (l), was burned in a calorimeter containing 1.500kg of water and at an initial temperature of 25.246°C, it was found that the molar enthalpy, ΔH°, was -5548 kJ/mol. Determine the final temperature of the water. (10)
11. What is the collision theory? Include the criteria for effective collisions. (3)
12. The standard heat of combustion of ethanol is -1372 kJ/mol ethanol. How much heat is released when 20.0g sample burns? (4)
13. A 0.1375g sample of solid magnesium is burned in a bomb calorimeter that has a heat capacity of 3024 J/°C. If the temperature of the calorimeter increased by 1.126°C, calculate the heat given off by burning the Mg in kJ/g and in kJ/mol (4)
14. Given the following experimental data: NO (g)
+
NO2 (g)
+
O2 (g)
→
N2O5 (g)
Trial [NO], M
Trial [NO2], M
Trial [O2], M
Initial Rate, Ms -1
1.25 x 103−
1.25 x 103−
1.25 x 103−
0.0087
2.50 x 103−
1.25 x 103−
1.25 x 103−
0.0174
1.25 x 103−
3.02 x 103−
1.25 x 103−
0.0508
1.25 x 103−
3.02 x 103−
3.75 x 103−
0.4570
a) Determine the rate law expression for this reaction. Show all work. (4)
b) Determine the rate law constant for this reaction. Include units. (3)
c)
If this reaction was carried out at the same temperature where [NO]= 3.01 x 10#3− , [NO2]=
1.00 x 10#3− , [O2]= 1.15 x 10#3− , determine the rate of the reaction (2)
15. From the following enthalpies of reactions determine the ΔH°, for: 2 HCl (g)
+
F2 (g)
→
2 HF (l)
+
Cl2 (g)
4 HCl (g) + O2 (g) → 2 H2O (l) + Cl2 (g)
ΔH = -148.4 kJ
1/2 H2 (g) + 1/2 F2 (g) → HF (l)
ΔH = -600.0 kJ
H2 (g) + 1/2 O2 (g) → H2O (l)
ΔH = -258.5 kJ
16. a) Determine the ΔH° for the target reaction below. Use the standard reduction potential given (3) Fe3O4 (s)
+
8 HCl (g)
→
2 FeCl3 (s) +
FeCl2 (s)
+
4 H2O (g)
b) Sketch an enthalpy graph for this reaction (5)
c) What would be the quantity of heat generated if 4.67 kg of Fe3O4 (s) was reacted? (3)
17. Given: H2 (g) + Br2 (l) → 2 HBr (g)
ΔH°= -72.8 kJ… Calculate the amount of energy
absorbed or released when 15.0g of HBr (g) is formed. (3)
18. Use the standard heats of formation to: a) Determine the enthalpy of reaction for: (3) Fe3O4 (s)
+
8 HCl (g)
→
2 FeCl3 (s) +
FeCl2 (s)
+
4 H2O (g)
b) Draw an enthalpy graph showing the change in enthalpy for the reaction and indicate if the reaction is exothermic or endothermic (5)
c) Determine the enthalpy change when 530.0g of HCl reacts with excess hydrogen chloride. (3)
19. Given the following thermochemical equation: 2 P (s) + 3 Br2 (l) → 2 PBr3 (s).….ΔH°= 153 kJ. How much energy must be added to allow the production of 7.12g of PBr3? (4)
20. An aqueous solution of calcium hydroxide, Ca(OH)2 [limewater], can be used to neutralize hydrochloric acid as follows: Ca(OH)2 (aq)
+
2 HCl (aq)
→
CaCl2 (aq)
Calculate the ΔH° for this reaction using the following equations (3) CaO (s) + 2 HCl (aq) → CaCl2 (aq)
ΔH°= -186 kJ
CaO (s) + H2O (l) → Ca(OH)2 (s)
ΔH°= -62.3 kJ
Ca(OH)2 (s) → Ca(OH)2 (aq)
ΔH°= -12.6 kJ
+
2 H2O (l)
2 21. For the reaction: 2 NO (g) + H2 (g) → N2 (g) + 2 H2O (l), the rate law is rate= k [NO]#[H 2].
Does the following proposed mechanism agree with this rate law? Explain your answer. (3) 2 NO (g) + H2 (g) → N2 (g) + H2O (l) + 1/2 O2 (g)
slow
H2 (g) + 1/2 O2 (g) → H2O (l)
fast
22. Using a Maxwell-Boltzmann curve, explain each of the following… a) The effect of temperature on the rate of a reaction (2)
b) Using a negative catalyst on the rate of a reaction (2)
23. For the reaction:
NO (g) + O3 (g) →
NO2 (g) + O2 (g)
a) Calculate the heat of reaction using the heats of formation provided (2)
b) Draw a potential energy diagram for this reaction. Label all parts, and include numerical data. Note: Ea= 63 kJ (4)
c) Using the balanced equation, calculate the change in heat when 276g of ozone reacts (3)
24. List and explain the 5 factors that affect the rate of a reaction. (10)
25. Using an enthalpy graph, describe the difference between an activated complex and a reaction intermediate (4)
26. Differentiate between potential energy, chemical bond energy and nuclear energy (6)
27. The mechanism for a reaction, the activation energy, and the heat of reaction of each step were experimentally determined for a reaction to be as follows: Elementary Steps
ΔHrxt (kJ/mol)
Ea (kJ/mol)
2A+B→C
400
-29
C+A→D+E
120
11
E+G→F
430
-31
F+B→H+G
50
-22
a) Which step would be the rate determining step? Give 2 reasons for your choice (2)
b) Write the overall thermochemical equation (2)
c) Is this reaction endothermic or exothermic? (1)
d) What is the role of G in the reaction mechanism (1)
e) Sketch the above reactions on a potential energy diagram and show the intermediate (4)