8. Thermochemistry

Thermochemical Equations

Writing Thermochemical Equations with Enthalpy Changes Sample Problem 1

How much heat in kilojoules is evolved or absorbed in each of the following reactions?(b) Reaciton of 4.88 g of barium hydroxid eoctahydrate with ammonium chloride: Ba(OH)2·8 H2O (s) + 2 NH4Cl (s) → BaCl2(aq) + 2 NH3(aq) + 10 H2O(l) ΔH° = +80.3 kJ

Nitromethane (CH3NO2), sometimes used as a fuel in drag racers, burns according to the following equation. How much heat is released by burning 100.0 g of nitromethane? 4 CH3NO2(l) + 7 O2(g) → 4 CO2(g) + 6 H2O(g) + 4 NO2(g) ΔH° = -2441.6 kJ

Reaction of gaseous fluorine with compound X yields a sin- gle product Y, whose mass percent composition is 61.7% F and 38.3% Cl. (d) How much heat in kilojoules is released or absorbed in the reaction of 25.0 g of X with a stoichiometric amount of F2, assuming 87.5% yield for the reaction?

Isooctane is the primary component of gasoline and burns in air to produce water rand carbon dioxide
2 C8H18(g) + 25 O2(g) → 16 CO2(g) + 18 H2O(l) ΔH°= —10,940 kJ
How much energy is released if 100.0 mL of isooctane (density = 0.690 g/mL) are burned
(a) 3300 kJ
(b) 6620 kJ
(c) 6950 kJ
(d) 3.02 kJ

Determine the mass of CO2 produced by burning enough
of each fuel to produce 1.00 * 102 kJ of heat. 
a. CH4( g) + 2 O2( g)¡CO2( g) + 2 H2O( g)
ΔH °rxn = -802.3 kJ

The propane fuel (C3H8) used in gas barbeques burns according
to the thermochemical equation:
C3H8( g) + 5 O2( g)¡3 CO2( g) + 4 H2O( g)
ΔH °rxn = -2044 kJ
If a pork roast must absorb 1.6 * 103 kJ to fully cook, and if only
10% of the heat produced by the barbeque is actually absorbed
by the roast, what mass of CO2 is emitted into the atmosphere
during the grilling of the pork roast?

When solutions containing silver ions and chloride ions are
mixed, silver chloride precipitates
Ag+1aq2 + Cl-1aq2 ¡ AgCl1s2 H = -65.5 kJ
(a) Calculate H for the production of 0.450 mol of AgCl by
this reaction. 
(b) Calculate H for the production of 9.00 g
of AgCl. 
(c) Calculate H when 9.25 * 10-4 mol of AgCl dissolves
in water.

The combustion of one mole of liquid octane, CH3(CH2)6CH3,
produces 5470 kJ of heat. Calculate how much heat is produced
if 1.000 gallon of octane is combusted. See Exercise 3.68
for necessary information about octane.

Consider the following reaction:&nbsp;2 C6H6 (l) + 15 O2 (g) → 12 CO2 (g) + 6 H2­O (g) &nbsp;&nbsp;∆Hº = – 6278 kJWhat volume of benzene (C6H6, d = 0.880 g/mL, molar mass = 78.11 g/mol) is necessary to evolve 5.19 x 109 kJ of heat?&nbsp;

Charcoal is primarily carbon. Determine the mass of CO2
produced
by burning enough carbon (in the form of charcoal)
to produce 5.00 * 102 kJ of heat.
C(s) + O2( g)¡CO2( g) ΔH °rxn = -393.5 kJ

At one time, a common means of forming small quantities of
oxygen gas in the laboratory was to heat KClO3:
2 KClO31s2¡2 KCl1s2 + 3 O21g2 H = -89.4 kJ
For this reaction, calculate H for the formation of (a) 1.36 mol
of O2

Liquid butane (C4H10) is stored in cylinders to be used as a fuel. The normal boiling point of butane is listed as -0.5 °C. (c) How much heat must be added to vaporize 250 g of butane if its heat of vaporization is 21.3 kJ/mol? What volume does this much butane occupy at 755 torr and 35 °C?

How much heat in kilojoules is evolved or absorbed in the reaction of 2.50 g Fe2O3 with enough carbon monoxide to produce iron metal? Is the process exothermic or endothermic? Fe2O3(s) + 3 CO2(g) → 2 Fe(s) + 3 CO2(g) ΔH° = -24.8 kJ

A gaseous fuel mixture contains 25.3% methane (CH4), 38.2%
ethane (C2H6), and the rest propane (C3H8) by volume. When
the fuel mixture contained in a 1.55 L tank, stored at 755 mmHg
and 298 K, undergoes complete combustion, how much heat is
emitted? (Assume that the water produced by the combustion is
in the gaseous state.)

How much heat in kilojoules is evolved or absorbed in the reaction of 1.00 g of Na with H2O? Is the reaction exother- mic or endothermic? 2 Na(s) + 2 H2O(l) → 2 NaOH(aq) + H2(g) ΔH° = -368.4 kJ

Thermochemical Equations and Using the energy term (heat of reaction) in mole-mass problem solving

Thermochemistry: Heat and Enthalpy

At one time, a common means of forming small quantities of
oxygen gas in the laboratory was to heat KClO3:
2 KClO31s2¡2 KCl1s2 + 3 O21g2 H = -89.4 kJ
For this reaction, calculate H for the formation of (b) 10.4 g of KCl.

Consider the following reaction: 
2 CH3OH1g2¡ 2 CH41g2 + O21g2 H = +252.8 kJ 
(d) How many kilojoules of heat are released 
when 38.5 g of CH41g2 reacts completely with O21g2 to form 
CH3OH1g2 at constant pressure?

The familiar "ether" used as an anesthetic agent is diethly ether, C4H10O. Its heat of vaporization is +26.5 kJ/mol at Calorimetry and Heat Capacity (Section 9.7)
9.76 What is the difference between heat capacity and specific heat? 9.77 Does a measurement carried out in a bomb calorimeter give
its boiling point. How much energy in kilojoules is required to convert 100 mL of diethyl ether at its boiling point from liquid to vapor if its density is 0.7138 g/mL?

Methanol 1CH3OH2 is used as a fuel in race cars. 
(c) Calculate the heat 
produced by combustion per liter of methanol. Methanol 
has a density of 0.791 g>mL.

Heat lost = &#x2212;Heat gained and &Delta;T=Tf&#x2212;Ti

 Correct on the intermediate final temperature. 

Heat lost = &#x2212;Heat gained and &Delta;T=Ti&#x2212;Tf

 There is not enough information to answer this question. 

 Since the mass and specific heat of each nail is the same, the calculation can be completed. 

 Consider two identical iron nails:  One nail is heated to 95&#x2103;, the other is cooled to 15&#x2103;.  The two nails are placed in a coffee cup calorimeter and the system is allowed to come to thermal equilibrium.  What is the final temperature of the two nails? 

A mixture of 2.0 mol of H2( g) and 1.0 mol of O2( g) is placed in a
sealed evacuated container made of a perfect insulating material
at 25 °C. The mixture is ignited with a spark and reacts to form
liquid water. Determine the temperature of the water.

Cytochrome, a complicated molecule that we will represent
as CyFe2+, reacts with the air we breathe to supply energy
required to synthesize adenosine triphosphate (ATP). The
body uses ATP as an energy source to drive other reactions
(Section 19.7). At pH 7.0 the following reduction potentials
pertain to this oxidation of CyFe2+:
O21g2 + 4 H+1aq2 + 4 e- ¡ 2 H2O1l2 Ered ° = +0.8
(b) If the 
synthesis of 1.00 mol of ATP from adenosine diphosphate 
(ADP) requires a ∆G of 37.7 kJ, how many moles of ATP are 
synthesized per mole of O2?

Nitromethane (CH3NO2) burns in air to produce significant
amounts of heat.
2 CH3NO2(l ) + 32 O2( g)¡2 CO2( g) + 3 H2O(l ) + N2( g)
ΔH °rxn = -1418 kJ
How much heat is produced by the complete reaction of 5.56 kg
of nitromethane?

What is the Third Law of Thermodynamics?

Aluminum metal reacts wiht chlorine with a spectacular display of sparks: 2 Al(s) + 3 Cl2(g) → 2 AlCl3(s) ΔH° = -1408.4 kJ How much heat in kilojoules is released on reaction of 5.00 g of Al?

How much energy in kilojoules is required to convert 100 mL of water at its boiling point from liquid to vapor, and how does this compare with the result calculated in Problem 9.68 for diethyl ehter? [ΔHvap(H2O) = + 40.7 kJ/mol]

How much heat in kilojoules is evolved or absorbed in the reaction of 233.0 g of calcium oxide with enough carbon to produce calcium carbide? Is the process exothermic or endothermic? CaO(s) + 3 C(s) → CaC2(s) + CO(g) ΔH° = 464.6 kJ

Methanol 1CH3OH2 is used as a fuel in race cars. 
(d) Calculate the mass of CO2 
produced per kJ of heat emitted.

Consider the decomposition of liquid benzene, C6H61l2, to 
gaseous acetylene, C2H21g2: 
C6H61l2 ¡ 3 C2H21g2 H = +630 kJ 
(b) What is H for the formation of 1 mol of acetylene?

At the end of 2012, global population was about 7.0 billion
people. What mass of glucose in kg would be needed to
provide 1500 Cal/person/day of nourishment to the global
population for one year? Assume that glucose is metabolized
entirely to CO21g2 and H2O1l2 according to the following
thermochemical equation:
C6H12O61s2 + 6 O21g2¡6 CO21g2 + 6 H2O1l2
H = -2803 kJ

A modified version of the stoichiometric chart can used for thermochemical equations.

When 10.00 g of phosphorus is burned in O2( g) to form
P4O10(s), enough heat is generated to raise the temperature of
2950 g of water from 18.0 °C to 38.0 °C. Calculate the enthalpy
of formation of P4O10(s) under these conditions.

Consider the following reaction:
2 CH3OH1g2¡ 2 CH41g2 + O21g2 H = +252.8 kJ
(b) Calculate
the amount of heat transferred when 24.0 g of CH3OH1g2 is
decomposed by this reaction at constant pressure.

Thermochemical Equations Example 1

How much heat in kilojoules is evolved or absorbed in each of the following reactions? (a) Burning of 15.5 g of propane: C3H8 (g) + 5 O2(g) → 3 CO2(g) + 4 H2O (l) ΔH°=-2220 kJ

Titanium reacts with iodine to form titanium(III) iodide,
emitting heat.
2 Ti(s) + 3 I2( g)¡2 TiI3(s) ΔH °rxn = -839 kJ
Determine the mass of titanium that react if
1.55 * 103 kJ of heat is emitted by the reaction.

Nitromethane (CH3NO2), sometimes used as a fuel for drag racing, burns according to the following reaction:&nbsp; 4 CH3NO2 (l) + 7 O2 (g) → 4 CO2 (g) + 6 H2O (g)&nbsp;+&nbsp;4 NO2 (g) &nbsp; &nbsp; &nbsp;∆Hº = – 2441.6 kJ How much heat is released by burning 125.0 g of nitromethane (MW:61.044 g/mol)?&nbsp;

It is estimated that the net amount of carbon dioxide fixed by
photosynthesis on the landmass of Earth is 5.5 * 1016 g>yr
of CO2. Assume that all this carbon is converted into glucose.
(a) Calculate the energy stored by photosynthesis on
land per year, in kJ.

Thermochemical Equation

The automobile fuel called E85 consists of 85% ethanol and
15% gasoline. E85 can be used in the so-called flex-fuel vehicles
(FFVs), which can use gasoline, ethanol, or a mix as fuels.
Assume that gasoline consists of a mixture of octanes (different
isomers of C8H18), that the average heat of combustion
of C8H181l2 is 5400 kJ>mol, and that gasoline has an average
density of 0.70 g>mL. The density of ethanol is 0.79 g>mL. (a)
By using the information given as well as data in Appendix C,
compare the energy produced by combustion of 1.0 L of gasoline
and of 1.0 L of ethanol.

Chemistry: Stoichiometry and Thermochemical Equations

What mass of natural gas (CH4) must burn to emit 267 kJ of
heat?
CH4( g) + 2 O2( g)¡CO2( g) + 2 H2O( g) ΔH °rxn = -802.3 kJ

Assume that 100.0 mL of 0.200 M CsOH and 50.0 mL of 0.400 M HCl are mixed in a calorimeter. The solutions start out at 22.50 °C, and the final temperature after reaction is 24.28 °C. The densities of the solutions are all 1.00 g/mL, and the specific heat of the mixture is 4.2 J/(g•°C). What is the enthalpy change for the neutralization reaction of 1.00 mol of CsOH in kJ?

The creation of liquid methanol is accomplished by the hydrogenation of carbon monoxide:&nbsp;CO (g)&nbsp;+&nbsp;2 H2 (g) → CH3OH (l)&nbsp; &nbsp; &nbsp; &nbsp;∆Hº = – 128.1 kJHow much heat (in kJ) is released when 125.0 g CO reacts with 2.32 x 102 g H2?

Consider the reaction that occurs on mixing 50.0 mL of 0.560 M NaHCO3 and 50.0 mL of 0.400 M NaOH at 25 °C. 
(c) How much heat (in joules) is liberated by the reaction? (Standard heats of formation are given in Appendix B.)

At 791 K and relatively low pressures, the gas-phase decomposition 
of acetaldehyde 1CH3CHO2 is second order in 
acetaldehyde. 
CH3CHO1g2S CH41g2 + CO1g2 
The total pressure of a particular reaction mixture was 
found to vary as follows: 
<TABLE> 
(c) If the volume of the reaction mixture is 1.00 L, what 
is the total amount of heat liberated (in joules) after a 
reaction time of 605 s?

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1. Intro to General Chemistry

2. Atoms & Elements

3. Chemical Reactions

4. BONUS: Lab Techniques and Procedures

5. BONUS: Mathematical Operations and Functions

6. Chemical Quantities & Aqueous Reactions

7. Gases

9. Quantum Mechanics

10. Periodic Properties of the Elements

11. Bonding & Molecular Structure

12. Molecular Shapes & Valence Bond Theory

13. Liquids, Solids & Intermolecular Forces

14. Solutions

15. Chemical Kinetics

16. Chemical Equilibrium

17. Acid and Base Equilibrium

18. Aqueous Equilibrium

19. Chemical Thermodynamics

20. Electrochemistry

21. Nuclear Chemistry

22. Organic Chemistry

23. Chemistry of the Nonmetals

24. Transition Metals and Coordination Compounds

[BOOK CHEM] Clutch Version

Hess's Law

Hess's Law involves the use of partial reactions in the determination of the overall enthalpy of reaction.

Nature of Energy

Thermochemistry is the study of matter and energy associated with chemical reactions or physical changes.&nbsp;

Endothermic & Exothermic Reactions

Endothermic and Exothermic Reactions involve the absorbing and releasing of thermal energy respectively.&nbsp;&nbsp;

Heat Capacity

Heat Capacity is the amount of heat required to change the temperature of a substance.&nbsp;

Thermochemical Equations&nbsp;involve a balanced chemical equation with a given enthalpy value.

Internal Energy

The Internal Energy of a system is the total energy from all forms of kinetic and potential energy.&nbsp;

Kinetic & Potential Energy

Mechanical Energy is the energy associated with an object's velocity (Kinetic Energy) and its position (Potential Energy).&nbsp;

Formation Equations

Formation Equations involve the standard states of elements combining to form 1 mole of product.

Enthalpy of Formation

The Enthalpy of Formation for an element is a key component in determining the enthalpy of reaction.&nbsp;

Thermal Equilibrium

Thermal Equilibrium involves two substances that are in physical contact reaching the same final temperature over time.&nbsp;

Constant-Pressure Calorimetry

Constant-Pressure Calorimetry uses a coffee cup calorimeter to determine the heat transfers occurring in a liquid solution.

Constant-Volume Calorimetry

Constant-Volume Calorimetry uses a bomb calorimeter and a combustion reaction to determine its enthalpy of reaction.&nbsp;

First Law of Thermodynamics

The First Law of Thermodynamics states that energy cannot be created nor destroyed, but instead is transferred.&nbsp;