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## Expressing amounts of energy in different energy

1. Expressing amounts of energy in different energy units is necessary to solve many chemistry problems. For practice, complete the following table.
The Joule (J) is the SI unit of energy.
1 calorie (cal) = 4.184 J
J cal kJ
656

132

0.736

B Expressing amounts of energy in different energy units is necessary to solve many chemistry problems. For practice, complete the following table.
The Joule (J) is the SI unit of energy.
1 calorie (cal) = 4.184 J
J kJ kcal
656

0.703

0.115

C. The nutritional label on the package indicates that a package of crackers contains 166 Calories. Express this value in kJ and in J.
kJ J

1 cal = 4.184 J

2. An automobile engine provides 632 Joules of work to push the pistons.
In this process the internal energy changes by -2966 Joules.

Calculate the amount of heat that must be carried away by the cooling system.
q = Joules

B. A chemical reaction is run in which 163 Joules of heat are absorbed and 262 Joules of work are done by the system.

Calculate the change in the internal energy of the chemical system.
E = Joules

C. An automobile engine provides 510 Joules of work to push the pistons and generates 2121 Joules of heat that must be carried away by the cooling system.

Calculate the change in the internal energy of the engine.
E = Joules

3. When 1 mole of H2(g) reacts with Cl2(g) to form HCl(g) according to the following equation, 185 kJ of energy are evolved.
H2(g) + Cl2(g) 2HCl(g)

Is this reaction endothermic or exothermic?

What is the value of q? kJ

B When 2 moles of H2S(g) react with O2(g) to form H2O(l) and SO2(g) according to the following equation, 1.12×103 kJ of energy are evolved.
2H2S(g) + 3O2(g) 2H2O(l) + 2SO2(g)

Is this reaction endothermic or exothermic?

What is the value of q? kJ

C. When 1 mole of CH4(g) reacts with H2O(g) to form H2(g) and CO(g) according to the following equation, 206 kJ of energy are absorbed.
CH4(g) + H2O(g) 3H2(g) + CO(g)

Is this reaction endothermic or exothermic?

What is the value of q? kJ

4. When H2S(g) reacts with O2(g) according to the following reaction, 518 kJ of energy are evolved for each mole of H2S(g) that reacts. Complete the following thermochemical equation.
2H2S(g) + 3O2(g) 2H2O(g) + 2SO2(g) H = kJ

B. When SO2(g) reacts with O2(g) according to the following reaction, 98.9 kJ of energy are evolved for each mole of SO2(g) that reacts. Complete the following thermochemical equation.
2SO2(g) + O2(g) 2SO3(g) H = kJ

C. When NH4NO3(aq) reacts to form N2O(g) and H2O(l), 150 kJ of energy are evolved for each mole of NH4NO3(aq) that reacts. Complete the following thermochemical equation.
NH4NO3(aq) N2O(g) + 2H2O(l) H = kJ

5. The following thermochemical equation is for the reaction of hydrogen(g) with chlorine(g) to form hydrogen chloride(g).
H2(g) + Cl2(g) 2HCl(g) H = -185 kJ
How many grams of H2(g) would have to react to produce 40.3 kJ of energy?

grams

B. The following thermochemical equation is for the reaction of Fe3O4(s) with hydrogen(g) to form iron(s) and water(g).
Fe3O4(s) + 4H2(g) 3Fe(s) + 4H2O(g) H = 151 kJ
When 62.7 grams of Fe3O4(s) react with excess hydrogen(g), kJ of energy are .

Hint: An amount of energy is expressed as a positive number. The sign indicates whether the energy is absorbed or evolved.

C. The following thermochemical equation is for the reaction of nitrogen monoxide(g) with hydrogen(g) to form nitrogen(g) and water(l).
2NO(g) + 2H2(g) N2(g) + 2H2O(l) H = -752 kJ
When 10.2 grams of nitrogen monoxide(g) react with excess hydrogen(g), kJ of energy are .

Hint: An amount of energy is expressed as a positive number. The sign indicates whether the energy is absorbed or evolved.

6. In the laboratory a student finds that it takes 158 Joules to increase the temperature of 14.7 grams of gaseousoxygen from 24.3 to 36.9 degrees Celsius.

The specific heat of oxygen she has measured is J/g°C.
B. In the laboratory a student finds that it takes 59.5 Joules to increase the temperature of 13.3 grams of solidchromium from 24.4 to 35.0 degrees Celsius.

The specific heat of chromium she has measured is J/g°C.

C. In the laboratory a student finds that it takes 164 Joules to increase the temperature of 11.0 grams of gaseousneon from 23.4 to 38.7 degrees Celsius.

The specific heat of neon she has measured is J/g°C.

7. What is the energy change when the temperature of 11.9 grams of gaseousoxygen is decreased from 39.3 °C to 21.8 °C ?

B.
What is the energy change when the temperature of 10.0 grams of solidchromium is decreased from 39.4 °C to 23.5 °C ?

C. How much energy is required to raise the temperature of 13.7 grams of gaseousneon from 24.9 °C to 38.4 °C ?

8. A sample of gaseousoxygen is heated with an electrical coil. If 191 Joules of energy are added to a11.9 gram sample and the final temperature is 39.3°C, what is the initial temperature of the oxygen?

B. A sample of solidchromium is heated with an electrical coil. If 71.2 Joules of energy are added to a 10.0 gram sample and the final temperature is 39.4°C, what is the initial temperature of the chromium?

C. A sample of gaseousneon is heated with an electrical coil. If 190 Joules of energy are added to a 13.7 gram sample initially at 24.9°C, what is the final temperature of the neon?

9. The standard enthalpy change for the following reaction is -1.10×103 kJ at 298 K.
Mg(s) + C(s,graphite) + 3/2 O2(g) MgCO3(s) ΔH° = -1.10×103 kJ
What is the standard enthalpy change for the reaction at 298 K?
2 MgCO3(s) 2 Mg(s) + 2 C(s,graphite) + 3 O2(g)
kJ

B. The standard enthalpy change for the following reaction is -258 kJ at 298 K.
Cd(s) + 1/2 O2(g) CdO(s) ΔH° = -258 kJ
What is the standard enthalpy change for the reaction at 298 K?
2 CdO(s) 2 Cd(s) + O2(g)
kJ

C. The standard enthalpy change for the following reaction is -206 kJ at 298 K.
2 C(s,graphite) + H2(g) + 3 Cl2(g) 2 CHCl3(g) ΔH° = -206 kJ
What is the standard enthalpy change for the reaction at 298 K?
C(s,graphite) + 1/2 H2(g) + 3/2 Cl2(g) CHCl3(g)
kJ

10. Given the standard enthalpy changes for the following two reactions:

(1) 4C(s) + 5H2(g) C4H10(g)…… ΔH° = -125.6 kJ

(2) C2H4(g) 2C(s) + 2H2(g)……ΔH° = -52.3 kJ

what is the standard enthalpy change for the reaction:

(3) 2C2H4(g) + H2(g) C4H10(g)……ΔH° = ?
kJ

B. Given the standard enthalpy changes for the following two reactions:

(1)2Pb(s) + O2(g) 2PbO(s)…… ΔH° = -434.6kJ

(2)Pb(s) + Cl2(g) PbCl2(s)……ΔH° = -359.4 kJ

what is the standard enthalpy change for the reaction:

(3)2PbCl2(s) + O2(g) 2PbO(s) + 2Cl2(g)……ΔH° = ?
kJ

C,.Given the standard enthalpy changes for the following two reactions:

(1) N2(g) + O2(g) 2NO(g)…… ΔH° = 181.8 kJ

(2) N2(g) + 2O2(g) N2O4(g)……ΔH° = 9.2 kJ

what is the standard enthalpy change for the reaction:

(3) 2NO(g) + O2(g) N2O4(g)……ΔH° = ?
kJ

11. Using standard heats of formation, calculate the standard enthalpy change for the following reaction.

CO2(g) + H2(g) CO(g) + H2O(g)

B. Using standard heats of formation, calculate the standard enthalpy change for the following reaction.

N2(g) + O2(g) 2NO(g)

C. Using standard heats of formation, calculate the standard enthalpy change for the following reaction.

NH4NO3(aq) N2O(g) + 2H2O(l)

12. A scientist measures the standard enthalpy change for the following reaction to be 84.2 kJ :

NH4Cl(aq) NH3(g) + HCl(aq)

Based on this value and the standard enthalpies of formation for the other substances, the standard enthalpy of formation of NH3(g) is kJ/mol.
B. A scientist measures the standard enthalpy change for the following reaction to be -344.2 kJ :

2Na(s) + 2 H2O(l) 2NaOH(aq) + H2(g)

Based on this value and the standard enthalpies of formation for the other substances, the standard enthalpy of formation of H2O(l) is kJ/mol.

C. A scientist measures the standard enthalpy change for the following reaction to be 560.5 kJ :

2BrF3(g) Br2(g) + 3 F2(g)

Based on this value and the standard enthalpies of formation for the other substances, the standard enthalpy of formation of BrF3(g) is kJ/mol.

13. Ethanol, C2H6O, is most often blended with gasoline – usually as a 10 per cent mix – to create a fuel called gasohol. Ethanol is a renewable resource and ethanol-blended fuels, like gasohol, appear to burn more efficiently in combustion engines. The heat of combustion of ethanol is 326.7 kcal/mol.

The heat of combustion of hexane, C6H14, is 995.0 kcal/mol. How much energy is released during the complete combustion of 318 grams of hexane ?
kcal
1.

Assuming the same efficiency, would 318 grams of ethanol provide more, less, or the same amount of energy as 318 grams of hexane?

B. Hydrocarbons, compounds containing only carbon and hydrogen, are important in fuels.

The heat of combustion of cyclohexane, C6H12, is 936.8 kcal/mol.

Write a balanced equation for the complete combustion of cyclohexane.
+ +

How much energy is released during the complete combustion of 371 grams of cyclohexane ?
kcal

C. Combustion reactions are exothermic. The heat of reaction for the combustion of cyclobutane, C4H8, is 650.3 kcal/mol. What is the heat of combustion for cyclobutane in kcal/gram?
kcal/gram

How much heat will be given off if molar quantities of cyclobutane react according to the following equation?
C4H8 + 6 O2 4 CO2 + 4 H2O

kcal

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