Download Review of 17.1, 17.2 and 17.3 Name: 1.) When 2 moles of NO burn

Review of 17.1, 17.2 and 17.3
Name: _____________________
1.) When 2 moles of NO burn in air to produce 2 moles of nitrogen dioxide, 113.04 kJ of heat is produced. Write a
balanced thermochemical equation for this reaction.
2NO
+
O2
→
2NO2
2NO
+
O2
→
2NO2
∆ H = -113.04 kJ
+
113.04 kJ
2.) Calculate the amount of heat produced when 34.8 g of methane, CH4, burns in an excess of oxygen, according to
the following equation.
CH4(g)
+
34.8 g CH4
2O2(g)
→
CO2(g)
1 mole CH4
16.0 g CH4
890.2 kJ
1 mole CH4
+
2H2O(l)
∆H = -890.2 kJ
= - 1.94 x 103 kJ
3.) State whether the following physical and chemical changes are endothermic or exothermic.
a) Melting
endothermic
d) fusion
endothermic
b) Vaporization endothermic
e) freezing
exothermic
c) Condensation
exothermic
f) combustion
exothermic
4.) How much heat is absorbed when 28.3 grams of ice at 00C is converted to liquid at 00C?
n water = 28.3 g
=
1.57 moles
18.02 g/mol
∆H = nH = (1.57 moles)(6.03 kJ/mole) = 9.45 kJ
5.) How much heat is absorbed when 5.53 moles of ammonium nitrate solid is dissolved in water?
Hsol’n = 25.7 kJ/mole
∆H = nH = (5.53 moles)(25.7 kJ/mole) = 142 kJ NH4NO3
6.) Calculate the amount of heat needed to melt 35.0 g of ice at 00C. Express your answer in kilojoules.
∆H = nH = (35.0 g/18.02 g/mol)(6.03 kJ/mol) = 11.7 kJ
7.) Calculate the amount of heat needed to convert 190.0 g of liquid water at 180C to steam at 100.00C. Draw a
heating curve to illustrate this.
8.) How much heat (kJ) is released when 2.543 moles sodium hydroxide is dissolved in water?
NaOH(s)
H2O (l)
→ Na+(aq) +
OH- (aq)
∆Hsol’n = -445.1 kJ/mole
∆H = nH
= - 1.132 x 103 kJ
9.) Calculate the amount of heat needed to convert 96 g ice at -240C to water at 280C. The specific heat capacity of
H2O(s) is 2.1 J/g 0C. Draw a heating curve to illustrate this.
10.) How can the enthalpy change be determined for a reaction in an aqueous solution?
a.
by knowing the specific heat of the reactants
b.
by mixing the reactants in a calorimeter and measuring the temperature change
c.
by knowing the mass of the reactants
d.
The enthalpy change for this type of reaction cannot be determined.
11.) During a phase change, the temperature of a substance ____.
a.
increases
c.
remains constant
b.
decreases
d.
may increase or decrease
12.) What are the four different methods used to communicate enthalpy changes?
1.) H - molar enthalpy (kJ/mole)____________________________________
2.) ∆H – enthalpy change (kJ)_______________________________________
3.) energy as a term in a balanced reaction_____________________________
4.) potential energy diagrams/enthalpy diagrams__________________________________
13.) Draw a potential energy diagram for this reaction.
2 NaHCO3(s) + 129 kJ →Na2CO3(s) + H2O(g) + CO2(g)
14.) If 22.0 mL of water containing 0.030 mol of HCl is mixed with 38.0 mL of water containing 0.030 mol of
NaOH in a calorimeter such that the initial temperature of each solution was 27.00C and the final temperature of
the mixture is 35.00C, how much heat (in kJ) is released in the reaction? Assume that the densities of the
solutions are 1.00 g/mL.
q = mc∆t
q = (60.0 g)(4.18 J/g 0C)(35.00C – 27.00C)
q = 2006.4 J = 2.01 x 103 J
Therefore H = - 2.01 kJ
15.) The following reaction is important in catalytic converters in automobiles. Rewrite this equation using the
∆H notation.
2CO(g) +
2NO(g)
→
N2(g)
+
2CO2(g)
+
2CO(g) +
2NO(g)
→
N2(g)
+
2CO2(g);
∆H = -746 kJ
746 kJ
Know:
1 Calorie = 1 kilocalorie = 1000 calories
q = mc ∆ t
∆H = nH
and for a bomb calorimeter
∆Etotal = C ∆ t
(where H = molar enthalpy in units of kJ/mole and H = heat of reaction for a given reaction in kJ)
Define the following Terms:
thermochemistry
chemical potential energy
surroundings
exothermic process
heat capacity
heat
system
endothermic process
specific heat
law of conservation of energy
calorimetry
calorimeter
enthalpy
thermochemical equation
heat of combustion
heat of reaction
molar heat of fusion
molar heat of solidification
molar heat of condensation
molar heat of vaporization
molar heat of solution
bomb calorimeter
Chapter 17 (Sec. 17.1, 17.3, and 17.2)
Chapter 17 (Sec. 17.1, 17.3, and 17.2)
Review Sheet 2
Review Sheet 2
1. Bricks in a fireplace will absorb heat and release it long after the fire has gone out. A student conducted an experiment to
determine the specific heat capacity of brick. Based on the evidence obtained in this experiment, 16 kJ of energy was
transferred to a 938 g brick as the temperature of the brick changed 19.5 oC to 35.0oC. Calculate the specific heat capacity of
the brick.
Q = mc ∆t
16 kJ = (938 g)(c)(35.0 – 19.50) = 1.1 J/g0C
2. In an investigation, ice at -25oC is converted to steam at 115oC at standard pressure.
(a) Draw a heating curve for the conversion if ice at -25oC to steam at 115oC.
(b) Label regions of the graph corresponding to temperature or phase changes
3. In a study of the properties of chlorine, chlorine gas at 25 oC and standard pressure is cooled to a temperature of
150oC.
(a) Sketch a cooling curve, including appropriate phase transition temperatures obtained from the periodic table.
(b) Label each section of the graph in part (a) with one of the labels q or ΔH.
(c) Label regions on your graph corresponding to kinetic and potential energy changes.
-
4. A hiker fills a pot with 2.39 kg of snow at -12.4oC and heats it over an open fire until it melts and is heated to 97.8 oC.
Calculate the total energy change for converting the snow to hot water.
qstep1= mc ∆t = 2390 x 2.01 J/g0C x 12.40C = 5.96 x 104 J
∆Hfus step2 = nHfus = (2390 /18.02)(6.03kJ/mol) = 8.00 x 10 5 J
qstep3 = mc ∆t = 2390 x 4.19 J/g0C x 97.80C = 9.79 x 105 J
TOTAL = 1.84 x 106 J = 1.84 x 103 kJ
5. Nuclear fusion reactors that produce energy from reactions similar to those that occur in the Sun are still at an
experimental stage. Calculate the total energy change required to change 1.00 t of water in a nuclear fusion reactor from 85oC
to steam at 250oC in a closed system at standard pressure.
2.6 x 106 kJ
q = mc ∆t = (1000000 kg)(4.19)(150C) = Joules
∆H = (1000000g/18.02 g/mol)(40.8 kJ/mol) = kJ
q = mc ∆t = (1000000 kg)(2.01)(1500C) = Joules
6. The molar enthalpy of combustion of natural gas is -802 kJ/mol. Assuming 100% efficiency and assuming that natural gas
consist only of methane, what is the minimum mass of natural gas that must be burned in a laboratory burner to heat 3.77 L of
water from 16.8oC to 98.6oC.
25.9 g
7. The molar enthalpy of combustion for a gasoline assumed to be octane is -1.3 MJ/mol. A particular engine has a heat capacity
of 105 kJ/oC. Assuming 100% efficiency, and assuming that gasoline consists only of octane, what is the minimum mass of
gasoline that must be burned to change the temperature of an engine from 18oC to 120oC?
0.94 kg
8. A 77.5 g piece of brass is heated to 98.7oC in a boiling water bath. The brass is quickly transferred to a calorimeter
containing 102.76 g of water at 18.5oC. The final temperature of the calorimeter and the brass is 23.5 oC. Calculate the specific
heat capacity of the brass.
0.369 J/g0C
Chem 122 – Review for Second Half of Chapter 17