# Exothermic Change and Chemistry Question

What is an exothermic change?one that takes place spontaneously
O one that requires heat energy from its surroundings
one that takes place very quickly
one that gives up heat energy to its surroundings
one that only takes place at very high temperatures
Use the References to access important values if needed for this question.
If the same amount of energy in the form of heat is added to 23.5 g samples of each of the metals
below, which metal will undergo the largest temperature change?
Metal
Ag
Al
Cu
Fe
Hg
Specific Heat Capacity (J/gXK)
0.235
0.897
0.385
0.449
0.140
ООООО
ARE
Ag
What is the energy change when the temperature of 12.3 grams of solid platinum is decreased from 36.0 °C to 20.2 °C ?
Joules.
Specific Heats (Csp)
Substance Formula Phase Csp (J/g°C)
TI
Diamond
С
solid
0.519
Gold
Au
solid
0.129
Graphite
С
solid
0.711
Helium
He
gas
5.19
Hydrogen
H2
gas
14.3
Iodine
| 12
solid
0.427
Iron
Fe
solid
0.444
Krypton
Kr
gas
0.247
Pb
solid
0.159
solid
1.017
Magnesium Mg
Mercury Hg
liquid
0.138
Neon
Ne
gas
1.03
Nickel
Ni
solid
0.444
Nitrogen
N2
gas
1.04
Oxygen
02
gas
0.916
Platinum
Pt
solid
0.133
Silicon
Si
solid
0.703
Silver
Ag
solid
0.237
Sulfur
S
solid
0.732
Tin
Sn
solid
0.213
Titanium
Ti
solid
0.523
Tungsten
W
solid
0.133
Uranium
U
solid
0.115
Water
H2O
liquid
4.184
Xenon
Xe
gas
0.158
Zinc
Zn
solid
0.388
In the laboratory a student finds that it takes 78.1 Joules to increase
the temperature of 15.0 grams of solid copper from 21.0 to 35.5
degrees Celsius.
The specific heat of copper calculated from her data is
J/g°C.
-g water
A 63.4 -g piece of lead at 95.0 °C was immersed into 75.0
at 25.0 °C. The water temperature rose to 26.8 °C. Calculate the
molar heat capacity of the metal.
0.131 J/mol.°C
113 J/mol.°C
6.47 J/mol.°C
27.1 J/mol.°C
25.8 J/mol. °C
A sample of solid diamond is heated with an electrical coil. If 93.9
Joules of energy are added to a 13.2 gram sample and the final
temperature is 38.0°C, what is the initial temperature of the
diamond?
°C.
The following information is given for water, H20, at latm:
boiling point = 100 °C AHvap(100 °C) = 40.7 kJ/mol
specific heat liquid = 4.18 J/g°C
At a pressure of 1 atm, what is AH in kJ for the process of
condensing a 23.8 g sample of gaseous water at its normal boiling
point of 100 °C.
kJ
Identify the point(s) on the following diagram where the
removal of heat will cause some of the sample to freeze .
F
G
H
Temperature
E
B
с
D
A
Heat Energy
Point(s);
The following information is given for bismuth at 1 atm:
Tb = 1627.00°C
AHvap (1627.00°C) =
822.9 J/g
AHfus (271.00°C) =
52.60 J/g
Tm = 271.00°C
Specific heat solid = 0.1260 J/g °C
Specific heat liquid = 0.1510 J/g °C
A 23.90 g sample of solid bismuth is initially at 252.00°C. If
the sample is heated at constant pressure (P = 1 atm),
kJ of heat are needed to raise the temperature of
the sample to 561.00°C.
When CO(g) reacts with O2(g) according to the following reaction, 283
kJ of energy are evolved for each mole of CO(g) that reacts. Complete
the following thermochemical equation.
2CO(g) + O2(g)—>2C02(g) AH =
kJ
When 12(g) reacts with Cl2(g) to form ICI(g), 26.8 kJ of energy are evolved for each mole of 12(g)
that reacts.
Write a balanced thermochemical equation for the reaction with an energy term in kJ as part of the
equation. Note that the answer box for the energy term is case sensitive.
Use the SMALLEST INTEGER coefficients possible and put the energy term (including the
units) in the last box on the appropriate side of the equation. If a box is not needed, leave it
blank.
+
+
+
The following thermochemical equation is for the reaction of iron(III)
oxide(s) with hydrogen(g) to form iron(s) and water(g).
Fe2O3(s) + 3H2(g)
→2Fe(s) + 3H2O(g)
+
ΔΗ = 98.8 kJ
When 44.6 grams of iron(III) oxide(s) react with excess hydrogen(g),
kJ of energy are
When a solid dissolves in water, heat may be evolved or
absorbed. The heat of dissolution (dissolving) can be determined
using a coffee cup calorimeter.
In the laboratory a general chemistry student finds that when 8.39
g of CsBr(s) are dissolved in 103.40 g of water, the temperature
of the solution drops from 24.64 to 21.98 °C.
Thermometer
Cardboard or
Styrofoam lid
The heat capacity of the calorimeter (sometimes referred to as the
calorimeter constant) was determined in a separate experiment to
be 1.87 J/°C.
Nested
Styrofoam cups
Reaction
occurs in
solution.
Based on the student’s observation, calculate the enthalpy of
dissolution of CsBr(s) in kJ/mol.
Assume the specific heat of the solution is equal to the specific
heat of water.
AH dissolution
kJ/mol
Calculate the AHⓇ for the following reaction using the information
below it.
C(s) + CH4(g) + H2(g) C2H6(g);
AH° ?
C(s) + 2 H2(g) → CH4(g);
AH° = -75 kJ
2 CH4(g) —— C2H6(g) + H2(g); AH° = 65 kJ
A. 140 kJ
B. 10 kJ
C. -10 kJ
D. -140 kJ
E. -85 kJ
Given the standard enthalpy changes for the following two
reactions:
(1) 4C(s) + 5H2(g)—*C4H10(g)
AH° = -125.6 kJ
(2) C2H4(g)
—2C(s) + 2H2(g) AH° = -52.3 kJ
what is the standard enthalpy change for the reaction:
(3) 2C2H4(g) + H2(g)—*C4H109) AH° = ?
kJ
A scientist measures the standard enthalpy change for the
following reaction to be -2917.0 kJ :
2C2H6() + 7 02(g)—>4CO2(g) + 6 H2O(g)
Based on this value and the standard enthalpies of formation
for the other substances, the standard enthalpy of formation of
CO2(g) is kJ/mol.
AVERAGE BOND ENTHALPIES (kJ/mol) AT 25 °C
Single Bonds
H C N 0 F Si s Ci Br I
H 436 413 391 463 565 318 322 347 432 366 299
C 413 346 305 358 485 — — 272 339 285 213
N 391 305 163 201 283
192 243
0 463 358 201 146 184 452 335
218 201 201
F 565 485 283 184 155 565 490 284 253 249 278
Si 318
452 565 222
293 381 310 234
P 322
335 490
201
326
184
S 347 272
284 293
226 255 213
CI 432 339 192 218 253 381 326 255 242 216 208
Br 366 285 243 201 249 310 213 216 193 175
I 299 213
201 278 234 184
208 175 151
Multiple Bonds
Double
Bonds
(kJ/mol)
Triple Bonds
(kJ/mol)
C=C
602 C=C
835
0=0
498
C=0
732 C=0
1072
N=0
607
N=N
418 NEN
945
C=N
615 C=N
887

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