Thermochemistry

1
Thermochemistry Rates Review
2
Thermochemistry Rates
TITLE A TITLE B TITLE C TITLE D TITLE D
100 100 100 100 100
200 200 200 200 200
300 300 300 300 300
400 400 400 400 400
500 500 500 500 500
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• The units for enthalpy change are
• a. kJ c. kJ/mol
• b. kJ/kgC d. kJ/LC

4
1A Answer 100

• a. kJ

5
Q2A Question 200

• What is the unit of rate constant, K, if it is a
  second- order reaction and the rate is measured
  in mol/L.s and concentrations in mol/L

6
2A ANSWER 200

• K L/mol

7
Q3A Question 300

• In the reaction CH4 2O2 ? CO2 2H2O
• The rate of consumption of oxygen gas is observed
  to be 4 mol/(L.min). What is the rate of
  production of CO2 gas?
• a)1 mol/(L.min)
• b) 2 mol/(L.min)
• c) 4 mol/(L.min)
• d) 8 mol/(L.min)

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3A ANSWER 300

• b) 2 mol/(L.min)

9
Q4A Question 400

• The rate of reaction depends upon
• a)The concentration and nature of the reactant
• b)The temperature of the reaction
• c)Whether or not a catalyst was used
• d)All of the above

10
4A Answer 400

• d)All of the above

11
Q5A Question 500

• Which of the following factors that affect rate
  of reaction applies only to heterogenous system
• Surface area
• Concentration
• Temperature
• catalyst

12
5A Answer 500

• a)Surface area

13
Q1B Question 100

• The catalytic converter on a vehicle is
• A biological catalyst
• Heterogenous catalyst
• A homozygous catalyst
• A reactant

14
1B Answers 100

1. Heterogenous catalyst

15
Q2B Question 200

• The activation energy of a chemical reaction is
  affected by
• The kinetic energy of the reactant
• The potential energy of the product
• The presence of a catalyst
• None of the above

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2B Answer 200

• The presence of a catalyst

17
Q3B Question 300

• If the initial rate of reaction is observed to
  increase by a factor of 9 when the concentration
  of a reactant is tripled, what is the order of
  reaction with respect to the reactant
• 0
• 1
• 2
• 3

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3B Answer 300

• c) 2

19
Q4B Question 400

• The gas phase reaction A B ?C has a reaction
  rate that is experimentally observed to follow
  the relationship rate KA2. What is the
  reaction order with respect to B
• 0
• 1
• 2
• 3

20
4B Answer 400

• a) 0

21
Q5B Question 500

• Which of the following statement is incorrect?
• The reaction rate for a zero-order reaction is
  independent of the concentration
• The rate constant for a second-order reaction is
  dependent on temperature
• The rate law expression relates rate and
  concentration
• The rate constant for a first-order reaction
  never varies with temperature or pressure

22
5B Answer 500

• d) The rate constant for a first-order reaction
  never varies with temperature or pressure

23
Q1C Question 100

• Which of the following corresponds to the
  equation for the standard molar enthalpy of
  formation of solid sodium chlorate, NaClO3
• a.Na(s) 1/2 Cl2(g) 3/2O2 ? NaClO3(s)
• b. 2Na(s) Cl2(g) 3O2(g) ?2NaClO3(s)
• c. Na(s) Cl(g) 3O(g) ? NaClO3(s)
• d. NaCl(s) 3/2 O2(g) ? NaClO3(s)

24
1C Answer 100

• a. Na(s) 1/2 Cl2(g) 3/2O2 ? NaClO3(s)

25
Q2C Question 200

• Which of these describes a reaction intermidiates
• Starting material
• A product
• Something formed and consumed during a reaction
• A step in a reaction mechanism

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2C Answer 200

• c) Something formed and consumed during a reaction

27
Q3C Question 300

• How many Kilojoules of heat is necessary to
  decompose 90 g of H2O(g) into H2(g) and O2(g) at
  ambient temperature and pressure
•  H2(g) O2(g) ? H2O (g)
  ?Hof -241.8KJ
•  
• 48.1 kJ
• 120.9 kJ
• 241.8 kJ
• d)1208 kJ

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3C Answer 300

• d) 1208 kJ

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• Q4C Question 400
• In a coffee-cup calorimeter, 50 ml of 1.0 mol/L
  HCl was neutralized by 50 ml of 1.0 mol/L NaOH.
  Initial temperature of both solutions were
  24.5oC. Final temperature after the reaction was
  75.5oC.
• Was the reaction exothermic or endothermic?
  Explain
• Calculate the mass of both solutions
• Calculate the temperature change
• Determine the thermal energy, q, released by the
  reaction.
• Calculate the number of moles of base in the
  reaction
• Calculate the molar enthalpy of neutralization,
  ?Hneut. Of the base.

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4C Answer 400

• Exothermic reaction. Increase in temperature of
  the surrounding
• 50 gm each
• 75.5 oC 24.5oC 51oC
• q mc?t 100g x4.18J/g.oC x51oC - 21.32kJ
• n C xV(L) 1.0mol/L x 50 ml/1000ml 0.05 mol
• q ?H n?Hneut q n?Hneut
• ?Hneut q/n
• - 21.32kJ
• 0.05 mol
• - 426.4 kJ/mol

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Q5C Question 500

• . In a coffee cup calorimeter, you place 15.0 mL
  of distilled water and measure the starting
  temperature to be 25?C. You then place 2.44 g of
  an unknown metal (initially heated up to 99.8?C)
  into the distilled water and insulate the
  calorimeter. After equilibrium, the final
  temperature of the water and the unknown metal is
  26.1?C.
• What is the specific heat (in J/g?C) of the
  unknown metal? The specific heat of water is
  4.184 J/g??C. Assume that no heat is transferred
  to the calorimeter. Show your starting
  equations, all of your calculations, and box in
  your final answer.

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• mw 15 ml x1 g/ml
  -qmetal qwater
• 15 g water
  (2.44 g x c x -73.7 oC) 68.97 J
• t1w 25 oC
  c 68.97 J
• t2w 26.1
  179.828 gxoC
• ?t w t2 t1
  
  0.3835 J/g.oC
• 26.1oC 25oC
• 1.1 o C
• cw 4.18J/g x oC
• qw mc?t
• 15 g x 4.18J x1.1oC
• g x oC
• 68.97 J
• m unknown m 2.44 g
• t1metal 99.8 oC
• t2 metal 26.1oC
• ?t metal 26.1oC 99.8 oC
• -73.7 oC
• qmetal 2.44g x c x -73.7oC

33
Q1D Question 100

• For the reaction A 2B ? 3C
• When the rate of appearance of C is 9 x 10-7
  mol/L.s, What will be the rate of disappearance
  of B?
• a) 2 x 10-7mol/L.s
• b) 12 x 10-7 mol/L.s
• c) 6 x 10-7 mol/L.s
• d) 9 x 10-7 mol/L.s

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1D Answer 100

• c) 6 x 10-7 mol/L.s

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Q2D Question 200

• In a reaction mechanism, the rate determining
  step is always
• a) The last step
• b) The slowest step
• c) The reaction intermediate
• d) The fastest step

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2D Answer 200

• b) The slowest step

37
Q3D Question 300

• True or false
• The instantaneous reaction rate is always
  constant.

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3D Answer 300

• False

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Q4D Question 400

• Pyruvic acid is a molecule involved as an
  intermediate in metabolic reactions such as
  cellular respiration. Pyruvic acid (CH3COCOOH)
  is converted into acetic acid and carbon monoxide
  in the reaction
• CH3COCOOH ? CH3COOH CO
•  If the molar enthalpies of combustion of these
  substances are, respectively 1275 kJ/mol, -875
  kJ/mol, and -282.7 kJ/mol, use Hesss law to
  calculate the enthalpy change for the given
  reaction. Hint write equations to represent the
  combustion reactions for the reactant and
  products. The given reaction above is the target
  equation

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• 1. CH3COCOOH 5O2 ? 3CO2 2H2O ?HCom 1275
  kJ
• -1 x 2. CH3COOH 2O2 ? 2CO2 2H2O ?HCom
  875 kJ x-1
• -1 x 3. CO 1/2O2 ? CO2
  ?HCom 282.7 kJ x-1
•  
• 1. CH3COCOOH 5/2O2 ? 3CO2 2H2O ?HCom1
  1275 kJ
• 2. 2CO2 2H2O ? CH3COOH 2O2
  ?HCom2 875 kJ
•  3. CO2 ? CO 1/2O2
  ?HCom3 282.7 kJ
•  Cancel molecules common to both sides
• Sum up the molecules and enthalpy change of three
  reactions
• ?H ?H Com1 ?HCom2 ?HCom2
• CH3COCOOH ? CH3COOH CO ?Hr
  117.3 KJ

41
Q5D Question 500

• A certain chemical reaction can be represented
  by the following equation.
• 2A(g) B(g) ? C(g)
• At a fixed temperature, the initial rate of the
  reaction was measured for various initial
  concentrations of A and B. The results were as
  follows
•  Initial Conc. (mol/L) Initial reaction Rate
  (mol/L.s)
• A B
• 0.5 0.5 2.0 x 10-3
• 1.0 0.5 8.0 x 10-3
• 1.0 1.0 8.0 x 10-3
• 1.5 1.0 18 x10-3
• 1.0 1.5 8.0 x 10-3
• The rate law expression for this reaction is
• a) Rate KAB
• b) Rate KB2
• c) Rate KA2B2
• d) Rate KA2

42
5D Answer 500

• d) Rate KA2

43
Q1E Question 100

• Similar elements tend to react similarly, but at
  different reaction rate.

44
1E Answer 100

• True

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Q2E Question 200

• The heat released during the combustion of
  C3H8(g) (propane) to produce CO2(carbon dioxide)
  gas and water vapour is 2222 kJ/mol of C3H8(g).
  Which of the following is the correct
• chemical equation for the reaction?
• a. C3H8(g) 5O2(g) ? 3CO2(g) 4H2O (g) ?H
  2222 kJ
• b. C3H8(g) 5O2(g) 2222 kJ ? 4H2O (g)
  3CO2(g)
• c. C3H8(g) 5O2(g) ?3CO2(g) 4H2O (g) 2222 kJ
• d. 3CO2(g) 4H2O(g) ? 5O2(g) C3H8(g) ?H 2222
  kJ
•  

46
2E Answer 200

• c. C3H8(g) 5O2(g) ?3CO2(g) 4H2O (g) 2222 kJ

47
Q3E Question 300

• According to the Rate Law, the rate (r) for the
  reaction
• aX bY ? product must be proportional to
•   a. X c. XaYb
• b. Y d. XmYn

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3E Answer 300

• d. XmYn

49
Q4E Question 400

• Consider the decomposition of hydrogen peroxide
  reaction. If the rate of decomposition of
  hydrogen peroxide at a particular temperature is
  determined to be 0.098 mol/(Ls), what are
• the rates of reaction with respect to the
  products of the decomposition reaction?
• Hint Be sure to write a balanced chemical
  equation to represent the reaction

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4E Answer 400

•  
• H2O2(l) ? H2(g) O2(g)
• ?H2O2(l) 0.098 mol/(L.s)
• ?t
•   ?H2O2(l) H2(g)
• ?t ?t
• O2(g)
• ?t
• H2(g) 0.098 mol/L.s
• ?t
•  O2(g) 0.098 mol/L.s
• ?t

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• DAILY DOUBLE

52
Q5E Question 500

• Insert Daily double question or picture here.

53
5E Answer 500

• Insert answer or picture choice here!