CHEM 1050 Chapter Notes - Chapter 6.1, 6.2, 6.3 and 6.6: State Function, Thermodynamics, Endothermic Process

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3 Feb 2017

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Nearly all chemical reactions involve either the release or the absorption of heat, a form of energy. Thermodynamics = the science of the relationships between heat and other forms of energy. Thermochemistry = one area of thermodynamics that concerns the study of the quality of heat absorbed or evolved (given off) by chemical reactions. Knowing such values, you are able to calculate the amount of energy needed to break a particular kind of chemical bond and so learn something about the strength of that bond. Heat measurements also provide data needed to determine whether a particular chemical reaction occurs and if so, to what extent. Energy = the potential or capacity to move matter. Energy is a property of matter not a material thing. Exists in different forms that can be interconverted. Energy can exist in different forms, including heat, light and electrical energy and these different forms can be interconverted.

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Experiment 11 ENTHALPY OF REACTION (HESS'S LAW) IDEAS Both the physical and biological worlds are characterized by a complex interplay of chemical reactions. In all chemical reactions, heat is released or absorbed. Combustion is one of the commonly observed chemical reactions accompanied by the evolution of heat energy, which may be harnessed of for such as the heating of homes, or which may be converted to other forms energy, such as mechanical energy in the steam engine or the internal combustion engine. One of the pioneering studies on the heat of chemical reactions was made by Lavoisier and ace in 1 Investigating the heat associated with various reactions, including combustion, they showed that each reaction was associated with a specific amount of heat and that the heat evolved in chemical reaction is equal to the heat absorbed in the reverse reaction. Lavoisier had proposed the modern theory of combustion as the combination of a substance with aygen. He also suggested the hypothesis that respiration is merely slow combustion. With Laplace, Lavoisier attempted to compare the quantity of heat given off by a burning candle with that given off by a live chicken. The quantity of heat was determined by measuring the quantity of ice that melted, in an insulated container, in the presence of the candle or the chicken. Little progress was made in thermochemistry until about fifty years later, when G. Hess (1802- 18500 studied heats of reaction in greater detail and stated the law a840) that bears his name: The heat evolved or absorbed in a chemical reaction is the same whether the process is accomplished in one step or in many. The law suggested, therefore, that both the reaction and the thermodynamic data could be treated algebraically. Although it was an empirical law when Hess proposed it, it was theoretically justified a few years later when the principle of conservation of energy was proposed. Hess's law can be illustrated by the following problem. Calculate the change in heat (AH) for the following reaction: 1. Mgo(s) 2H+(aq) Use the following information to solve the problem: AH- -35 kl/mole AH -56 kJ/mole 3, H+(aq) oHraq)

Practice problems for exam 2 ______________

Useful Information:

h=6.626Ã10-34JÂ·s.; c=3.0Ã108 m/sec; E=hï® ; E= hc , ï¬ = h/mv; 1J = 1 kg-m2/s2 ï¬

mass of electron = 9.11 Ã 10-28 g, ïE= q + w ; 1 cal = 4.184 Joules Please Show all Work

1. Which of the following substances have standard heats of formation that are equal to zero by definition (circle your answers): H2(g), H(g), O3(g), H2O(s), H2O(l), Hg(l), Hg(s), Hg(g).

2. Limestone stalactites are formed in the reaction: Ca2+(aq) + HCO3-(aq) ï CaCO3(s) + CO2(g) +

H2O(l)
If one mole of CaCO3 is produced at 298 K under one atmosphere of pressure, the reaction performs 590 calories of expansion work, pushing back the atmosphere as CO2 is formed. At the same time, 9310 calories of heat are absorbed from the environment. What is ïE in Kcal/mole for CaCO3.

3. What is the minimum wavelength of light in AÌ (1 AÌ = 10-8 cm) needed to provide enough energy per quantum to rupture the chemical bond in hydrogen iodide (HI). The bond dissociation energy of HI is 71.4 Kcal/mole.

4. Sketch the shape and orientation of the following types of orbitals: s, px, dxy, dz2, dx2-y2

5. Give the values of (n) , (l) and (ml) for each orbital in the 4p subshell.

6. Write the complete electron configuration for the following: Ti 2+_____________________________________ Cr_______________________________________

N______________________________________

7. Calculate the standard enthalpy of formation ( ï Ho) for diamond from graphite [i.e. C (graphite) ï C (diamond)] given that:

C (graphite) + O2 ï CO2 (g) ( ï Ho = -393.5 KJ/mole) C (diamond)] + O2 ï CO2 (g) ( ï Ho = -395.4 KJ/mole)

If 1.0g of graphite is converted to diamond, what is the energy change? Is this an endothermic or exothermic reaction?

8. An 160 pound astronaut on his way to Mars is buzzing along at 10,000 miles per hour. (a) Express his weight in grams (one pound = 454 grams) so that you can calculate the astronautâs wavelength (1mile/hour = 44.7 cm/sec)

(b) Suppose the astronaut detects outside his spacecraft a proton (m=1.7 x 10-24 g) from a âsolar windâ moving at exactly the spacecraft velocity. What is the proton wavelength is in AÌ (1 AÌ = 10-8 cm.

9. What is the maximum number of electrons that can occupy each of the following subshells? a) 3d_________________ b) 1s____________________ c) 2p ____________________

10. Identify the element represented by the following electronic configuration.

a) [Ne] 3s2____________________

b) What is the electron configuration for the first excited state of this atom.______________

11. Determine the number of valence electrons for each element.
(a) Br___________ (b) Na _________ (c) Sn __________

12. 175 g of Fe at 15.0oC is mixed with 225 g of H2O at 95.0oC. What is the final temperature of the mixture? The specific heats of iron= 0.448 J/g oC and water = 4.184 J/g oC). (keep in mind the following: heat gained + heat lost = 0 and q=mass x heat capacity x ïT)

13. (5 pts) Calculate values of ÎHrxn for the following reactions: CS2(g) + 3O2(g) ï® CO2(g) + 2SO2(g)

The heat of formation for the following substances is given in kJ/mol:

CS2 CO2 SO2 117.4 -393.51 -296.83

14. (6 pts) Use the electron configuration of Li and Be and determine which element has the greatest second ionization energy. Defend your answer.

15. Mark beside each of the following processes either âexoâ or âendoâ according to whether you think the process will release heat or absorb heat.

a. Ca(g) ï Ca(g)+2 + 2e-
b. I(g)+1e-ï I(g)-1
c. Ca(g)+2 + S(g)-2 ï CaS(s) d. I2(g)ï 2I(g)

( ) ( ) ( ) ( )

16. (6 pts) In each of the following pairs, which of the two species is larger?
a) O-2 or Na+ b) Ti+4 or Ti+2 c) B or C d) N or N-3

17. Write down the Lewis dot structure for the following (a) N_______________ (b) Ne________________

18. THE BORN HABER CYCLE: I may have a problem on the Born Haber cycle. Please check my lecture notes to see how to set up the process and then calculate the lattice energy from the various thermodynamic quantities such as in the NaCl example below;

ï H ï¯ f NaCl = -411KJ

Na(s) ï® Na(g) ï H =108KJ
1â2 Cl2 ï® Cl(g) ï H = 122KJ Ionization Energy of Na ï H = 496 KJ Electron affinity of Cl ï H = -349KJ

7.
Calculate the percentage, by mass, of fluorine in sulfurhexafluoride (SF6), a potent greenhouse gas.
A) 78.0%
B) 59.2%
C) 22.0%
D) 82.1%
E) 85.7%

8.
Octane (C8H18) is one of the principal components of gasoline. Howmany moles of CO2 are produced during the combustion of 3.0 mol ofoctane?
Unbalanced equation: C8H18 + O2 --> CO2 + H2O
A) 3.0
B) 26
C) 24
D) 8.0
E) 4

9.
How many atoms are present in 0.375 mol of palladium (Pd)atoms?
A) 6.23 x 1021
B) 2.26 x 1023
C) 6.02 x 1023
D) 1.61 x 1024
E) 2.12 x 1021

10.
How many molecules are present in 1.0 kg of hydrogen (H2)gas?
A) 6.0 x 1023
B) 3.0 x 1026
C) 6.0 x 1026
D) 3.0 x 1023
E) 1.7 x 1025

11.
What evidence indicates that the rising atmospheric CO2 levels arecaused by the combustion of fossil fuels?
A) Both the average global temperature and the atmospheric CO2level have risen.
B) The 14C/12C ratio in atmospheric CO2 is unusually low.
C) Increased precipitation in most of the NorthernHemisphere.
D) The 18O/16O ratio in atmospheric CO2 is the same as inatmospheric oxygen.
E) The level of atmospheric moisture has increased.

12.
Heat is a form of
A) Energy
B) Pressure
C) Work
D) Volume
E) Temperature

13.
Oxygenated gasolines
A) Are gasolines that have oxygen gas bubbled through them
B) Contain nitrogen containing compounds
C) Are formulated to contain water
D) Have higher activation energies for combustion than regulargasolines.
E) May contain MTBE or ethanol

14.
A chemical reaction accompanied by a release of energy is calleda/an ______ reaction.
A) exothermic
B) fast
C) activated
D) catalyzed
E) endothermic

15.
The diagram below shows a simplified version of a fractionatingcolumn used in the petroleum industry.

The compounds with the lowest boiling points are condensed atposition

A) C.
B) D.
C) B.
D) A.

16.
Where is most of the carbon on earth stored?
A) in the form of fossil fuels
B) in the deep ocean
C) in the atmosphere
D) in surface water
E) in the forests and soil

17.
Find the molar mass of ethanol, C2H6O.
A) 22.1 g/mol
B) 26.0 g/mol
C) 46.07 g/mol
D) 45.06 g/mol
E) 29.02 g/mol

18.
Determine the shape or geometry of PH3. (Hint: Use the PeriodicTable to arrive at the electron configuration forphosphorous.)
A) trigonal planar
B) linear
C) trigonal pyramidal
D) bent
E) tetrahedral

19.
The energy stored in the chemical bonds of fossil fuels is a formof ______ energy.
A) nuclear
B) potential
C) mechanical
D) kinetic
E) electrical

20.
The heat of combustion of methane, CH4, is 50.1 kJ/g. How much heatwould be generated if 1.00 mol of methane undergoes completecombustion?
A) 50.1 kJ
B) 804 kJ
C) 601 kJ
D) 0.32 kJ
E) 3.12 kJ

21.
Methane is approximately 23 times more powerful than carbon dioxideas a greenhouse gas. Which are significant sources of methaneemissions?
I. The digestive systems of ruminants (cows, sheep, etc.)
II. Automobile exhaust
III. Rice cultivation
IV. Decaying wetland vegetation
A) I and II only
B) I only
C) All of these
D) II only
E) I, III, and IV only

22.
Which atmospheric component does not contribute to globalwarming?
A) CH4
B) CO2
C) CFC
D) N2
E) H2O

23.
What is the effect of infrared energy on matter?
A) It breaks chemical bonds.
B) It excites bonding electrons.
C) It increases molecular rotation.
D) It increases the vibration of chemical bonds.
E) It excites non-bonding electrons.

24.
According to current estimates, the fuel in greatest abundance onearth is
A) natural gas.
B) hydrogen
C) uranium.
D) coal.
E) petroleum.

25.
A gasoline's octane rating is a measure of the
A) purity of the gasoline.
B) energy content of the gasoline.
C) percent of gasoline that contains octane
D) pollutants produced by burning the gasoline in a vehicle'sengine.
E) gasoline's resistance to causing knocking in a vehicle'sengine.

26.
Advertising claims sometimes state that adding something mechanicalto a car's engine will allow it to recover 100% of the energy thatcomes from burning gasoline. You should be skeptical of such claimsbecause they are not consistent with the
A) first law of thermodynamics.
B) energy difference between reactants and products
C) second law of thermodynamics.
D) law of conservation of matter.
E) activation energy requirements of all chemical reactions.

27.
In order to make useful predictions, which factors must beaccounted for by climatic models?
I. Cooling effect of atmospheric aerosols
II. Smoke, haze, and cloud cover
III. Change in land use
IV. Combustion of fossil fuels
A) III and IV only
B) II, III, and IV
C) II and III only
D) I, II, III, and IV
E) IV only

28.
Use the equation to help you calculate the heat of combustion ofethylene, C2H4. The bond energies are: C H 416 kJ/mol; C C 598kJ/mol; O O 498 kJ/mol; C O 803 kJ/mol; H O 467 kJ/mol.

The heat of combustion of ethylene is

A) 1216 kJ/mol.
B) 220 kJ/mol.
C) 1324 kJ/mol.
D) 754 kJ/mol.
E) 242 kJ/mol.

29.
Scientists believe they know the average global temperature overthe last 160,000 years. Which property of the ice core samples fromAntarctica provides this information?
A) the 1H/2H ratio
B) the density of the ice
C) the thickness
D) the temperature
E) the carbon dioxide concentration

30.
(Both the Clinton) and the George W. Bush administrations have beenunwilling to sign the Kyoto Protocol. What has been a stated reasonfor their objection to the treaty?
A) Enforcement of the treaty will be impossible.
B) Lack of conclusive evidence that increased atmospheric CO2 leadsto global warming.
C) The target emission levels are not sufficiently low to affectthe greenhouse effect.
D) The treaty does not include a provision for trading emissionallowances.
E) Developing countries are not required to control greenhouse gasemissions.

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CHEM 1050 Chapter Notes - Chapter 6.1, 6.2, 6.3 and 6.6: State Function, Thermodynamics, Endothermic Process

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