Unit 14 HW
Name
Page 1 of 12
Period
CRHS Academic Chemistry
Unit 14 Thermochemistry
Homework
Due Date
Assignment
On-Time (100)
Late (70)
14.1
14.2
14.3
Warm-Up
EC
Notes, Homework, Exam Reviews and Their KEYS located on CRHS Academic Chemistry
Website: https://cincochem.pbworks, corn
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Unit 14 HW
Unit 14 HW
14.1
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WHAT IS THERMOCHEMISTRY
.
[
2. What is the !aw of conservation of energy? ÿ ,,ÿ, ,ÿ::ÿ,ÿ ÿ k4,
3. Explain from where the heart in an eÿ(othermic reaction comes. ÿ-JÿPÿQJÿUv'ÿ
4, Describe the direction of heat flow.
°
"ÿi:'ÿ ÷'ÿ' ÿ,i
Classify these processes as exothermic or endothermic. (Think about whether the "object" is gaining or releasing
heat.)
A, Burning rubbing alcohol
B. Cooking an egg
(ÿ!ÿpxothermieo] endothermic )
( exothermic / eJqdothermic')ilÿ
C. Combustion of gasoline
;(exothermicl) endothermic)
a,
.... : ,
6. Indicate whether AH is positive (+) or negative (-) for the following:
A. the reactants have > enthalpythan the products AH = __
B. the products have >enthalpythanthe reactants AH = -ÿ
C. the surroundings lose heat as a reaction occurs AH =
D. the temperature increases as a reaction occurs
,
200
PE
(k J) 150
Label the graphs as endothermic or exothermic.
100
80-
100
PF. 60
(k J) 40 -
5O
20-
"ÿ
AH = __
a2
250
© ÿ9
C+D
Page 4 of 12
Unit 14 HW
14.2 ENTHALPIE5 OF REACTION
,
Why is Calorimetry important to the study of Thermochemistry? /k:CÿJÿ)
.
What is the key principle of Calorimetry? ÿJÿC ÿ
ÿ%, /1:ÿ ÿ ÿ
V,ÿ'%ÿ :ÿ ÿYÿ
:
/
Determine the AH for the following reactions and indicate with X if Exothermic or Endothermic
f
3. N2Ig) + 021g) + 43,3 kJ --) 2 &H=
NO(g) ÿ ÿ ÿ ÿ ÿ'4 Exothermic
2 C2H6 (g) + 02 Ig) --) 4 C02 (g) + 6 H20 (I) + 683.5 kJ
5. C3Hs(g) --> C3H8(I) + 41,8 Id
&H = ,
.
Exothermic
or Endothermic:iÿ ?
ÿ or Endothermic
or Endothermic
Rewrite. the following equations by expressing the energy change as a term in the equation:
6.
.
H20 (g)
AI
AH = -10.76 kJ
--) H20 (I)
+ 302 -'-)
2AI203
AH = -803.8kJ
Each of the following equations (with the ZIH provided) has been rewritten. Find the ZlH for the new equation.
6, Given: CuO(ÿ) --) Cu(ÿ) + 1/2 021ÿ)
2Cu(s)+ O2(g) "-) 2CuOis)
.
Given: 4 Fe Is) + 3 02 (g) ---) 2 Fe203 (s)
2 Fe Is) + 3/20ÿ (g) --) Fe203 Is)
.
AH = 37.1 kJ
AH=__
AH = -393.0 kJ
AH=
%<
Given: C2H2 + 5/2 02 -) 2 C02 + H20/I) + 379 kJ
2 C2H2 (g) + 5 O2(g) "--ÿ 4 CO2 (g) + 2 H20 (I)
.
Given: H2(g)+ Br2(g) ---) 2 HBr(g) + 17.3 Id
HBr(g) -> 1/2 H2(g) + 1/2 Br2ig)
AH=
t ÿ,,.:
?
Unit 14 HW
Page 5 of 12
Using each o/ the methods described on page 8 and 9 o/ Unit 14 Notes, apply Hess's Law and calculate the Enthalpy of
Reaction (AH°) /or problems 10-11,
Method A - Combination o/ thermochemical equations
Method B - AH° = sum of [(AHf° of products) x (tool of products)] - sum of [(AHf° of reactants) x (mol of reactants)]
i0. 2 H202(I) ÿ
Given:
2 H20 (I) +
O2(g)
H2(g) + O2(g) --) H202(I) AHf° = -187.8 kJ
J-O q- .20(./A.,°---28s.8 ,J
Method A
.,
/
,, :ÿ:I
'i
'
!Tt ÿ:V
%
Method B///
11. CaCO3 (s) "-) CaO (s) + CO2(G)
Given:
Ca (s) + C(s) + 3/2 02 (g) --) CaCO3 (s) AHf° = -1207 kJ
Ca (s) + O2 (g) --) CaO (s) AHf° = -636 Id
C (s) + ½ 02 (g) "-) CO2 (g) AHf° = --393 kJ
Method A
Method B
\
,ÿ
(
\
Page 6 of 12
Unit 14 HW
14.3 DRIVING FORCES FOF CHEMCIAL REACTIONS
1. In nature, reactions tend to proceed in a direction that leads to
,
©!ÿ:ÿ'ÿ energy state.
,ÿ ,ÿ}dÿd ÿ,ÿ d,,ÿ fÿ)
77fi+,.o
Explain why some endothermic reactions do occur
X!
L
4. In nature there is tendency to proceed in direction thit IICREAIEIÿy DECREASES the randomness of a
system.
5. Chemical reactions tend to go in direction(of IEOIIASIII311NCREASING order.
,/
.
Predict whether the value of AS for each of the following reactions will greater than, less than, or equal to zero.
C3CO2(s) + 502(g) ÿ 3 CO2(g) + 4 H20(g)
ÿ {ÿ}ÿ
302 (g) + P2 (g) --} 2 PO3 (g)
s
NaCl (s) -) Na+l(aq) + Cl-l(aq)
2Ca (s) + Clÿ (g) -> 2 CaCIÿ (s)
ÿ4##
d ..... !:,>,
7. Decide if AG can ever be negative and therefore the reaction is spontaneous and fill in 3ÿ column with conclusions.
AH
AG
AS
- value (exothermic)
+ value (more random)
- value (exothermic)
- value (less random)
+ value (endothermic)
+ value (more random)
+ value (endothermic
-value (less ransom)
Predict whether the reactions will be spontaneous at 298K by calculating AG° from the given enthalpies and entropies.
,
,
AH° = -+176 Id/mol and AS°= +0.2857 kJ/(mol*K)
AS°= 0.00300 kJl(mol*K)
Unit 14 HW
Page 7 of 12
Extra Credit- THERMOCHEMISTRY
1-11-1
' III-1E31-11-1 I-1
°
FI I---ll---II-]l-ll-l f-1
L,IN
1-11-1
Across
3. in an endothermic
reaction heat is
6.1 calorie = 4.184
8. heat flows from a
obiect to a cooler
object
fN
LII IN N F
NNNNFT]NNNF]
IIIIIIiNIN
9. accurate and precise
measurement of heat
change in a reaction
11,
type of energy
stored in chemical or
nuclear bonds
12.
heat flows out of
system - system warms -
negative change in enthalpy
15.
type of energy - a
type of potential energy
stored in bonds between
atoms in a substance
17,
heat of a system at
constant pressure
19.
type of energy -
total of all energy of
position and movement of
the particles in a system
21.
type of energy -
due to motion
Down
1. substance on right side of reaction
2. a
equation must be balanced
4. capacity for doing work or supplying heat
5. heat capacity is an
property of matter
7. change in enthalpy of a reaction is the same with one step or many steps (answer is HESS'S
LAW)
lO.heat enters the system - system cools - positive change in enthalpy
13.water has a
specific heat capacity (c)
14.water can hold a
amount of heat
16.substance on left side of reaction
18.energy that transfers from one object to another because of temperature difference
20.In an exothermic reaction heat is
Page 8 of 12
Unit 14 HW
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