WORKSHEET ON CHEMICAL REACTIONS AND ENERGY – I
1. Calculate the change in internal energy of the system and determine whether the process is endothermic or exothermic for a chemical reaction in which 10.0 kJ of heat is absorbed while the system does no work on the surroundings.
2. For a process in which the internal energy does not change, which of the following are possible?
(i) heat > 0, work < 0 (ii) heat > 0, work > 0
(iii) heat < 0, work < 0 (iv) heat < 0, work > 0
3.Calculate the change in internal energy of the system for the following process:
A balloon is heated by adding 320 J of heat. It expands, doing 180 J of work on the atmosphere.
4. For which of the following reactions at 25 °C would the enthalpy change represent a standard enthalpy of formation? For those where it does not, what changes would it need to be made in the reaction conditions?
A) 2Na(s) + 1/2O2(g) à Na2O(s)
B) 2K(l) + Cl2(g) à 2KCl(s)
C) C6H12O6(s) à 6C(diamond) + 6H2(g) + 3O2(g)
5.Write the equation corresponding to the standard enthalpy of formation of liquid carbon tetrachloride.
6. Which one of the following reactions has a positive value of H°?
A) NH3(g) --> NH3(l) B) CO2(g) --> CO2(s)
C) 2H2O(l) --> 2H2(g) + O2(g) D) C(s) + O2(g) --> CO2(g)
7. The value of H° for the following reaction is -126 kJ. Determine the amount of heat (in kJ) that would be evolved by the reaction of 25.0 g of Na2O2 with water.
2Na2O2(s) + 2H2O(l) --> 4NaOH(s) + O2(g)
8. When 0.215 mol NH3 is formed from nitrogen and hydrogen, 9.91 kJ of energy is released as heat. Assuming constant pressure is maintained, what is the H for this reaction per mole of NH3 formed?
9. For which one of the following reactions is the value of H° not equal to Hf° for the product?
A) 2C(s) + 2H2(g) --> C2H4(g) B) Ca(s) + 1/2O2(g) --> CaO(s)
C) C(s) + 1/2O2(g) --> CO(g) D) 3Mg(s) + N2(l) --> Mg3N2(s)
10. Which of the following changes always results in a negative U?
A) The system absorbs heat and has work done on it.
B) The system gives off heat and does work.
C) The system gives off heat and has work done on it.
D) The system absorbs heat and does work.
11. Substance Hf° (kJ/mol)
SO2(g) - 297
SO3(g) - 396
Determine the value of H° in kJ for the following reaction: 2SO2(g) + O2(g) --> 2SO3(g)
12. Substance Hf° (kJ/mol)
CaO(s) - 635.5
CO2(g) - 393.5
CaCO3(s) à CaO(s) + CO2(g) ΔH°= +178.1 kJ
Calculate the standard enthalpy of formation of CaCO3(s).
13. Use the following thermochemical equations
C2H2(g) + 5/2O2(g) --> 2CO2(g) + H2O(g) H° = -1300 kJ
C2H6(g) + 7/2O2(g) --> 2CO2(g) + 3H2O(g) H° = -1560 kJ
H2(g) + 1/2O2(g) --> H2O(g) H° = -286 kJ
to calculate H° for the following reaction:
C2H2(g) + 2H2(g) --> C2H6(g)
14. 2H2(g) + O2(g) à 2H2O(l) ΔH°= - 572kJ
The total volume of hydrogen gas needed to fill the Hindenburg was 2.0x108L at 1.0atm and 25°C. How much heat was evolved when the Hindenburg exploded, assuming all of the hydrogen reacted?
15. From the following enthalpies of reaction,
H2(g) + F2(g) --> 2HF(g) H = -537 kJ
C(s) + 2F2(g) --> CF4(g) H = - 680 kJ
2C(s) + 2H2(g) --> C2H4(g) H = +52.3 kJ
calculate H for the reaction of ethylene with F2:
C2H4(g) + 6F2(g) --> 2CF4(g) + 4HF(g)