CHEM 1215 – Unit 1 Practice Problems

 

1.       Convert 1.525 kcal to kJ.

 

2.      A closed system absorbs 125 J of heat from the surroundings while it performs 0.110 kJ of work.  What is the change in internal energy for the system?

 

3.      If the volume of a cyclinder increases from 1.50 L to 4.50 L at a constant pressure of 1.25 atm while it absorbs 1.515 kJ of heat, what is the change in internal energy of the system?  (1 atm-L = 101.3 J)

 

4.      Calculate the enthalpy change that occurs when 2.5 g of KClO3 decomposes according to the reaction:  2 KClO3 (s) à  2 KCl (s)  +  3 O2 (g)   DH = -89.4 kJ

 

5.      Calculate the enthalpy change that occurs when 7.4 g of KClO3 is formed according to the reaction in question 4.

 

6.      The specific heat of iron is 0.108 cal/g-K.  How much heat in kJ is needed to bring the terperature of 0.250 moles of iron from room temperature (25oC) to its melting point (1535oC)?

 

7.      What is the specific heat of copper if 1.376 kJ of heat must be added in order to raise the temperature of 55.0 g of copper from 22.5oC to 87.5oC.

 

8.      A 26.4 g sample of metal at 99.0oC is added to 25.0 g of water in a constant pressure calorimeter.  If the initial temperature of the water was 20.0oC and the equilibrium temperature is 27.0oC, what is the specific heat of the metal?  What is the molar heat capacity of the metal if its molar mass is 63.5 g/mol?  (Cs for water = 4.18 J/g.K)

 

9.      When 5.0 g of KBr is dissolved in 30.0 g of water, the temperature drops from 21.0oC to 15.3oC.  What is the molar heat of solution of KBr in kJ/mole?  Assume that the specific heat of the solution is 4.18 J/g.K.

 

10.   A 1.276 g sample of propane (C3H8) is burned in a bomb calorimeter with a heat capacity of 7.850 kJ/K.  If the temperature of the calorimeter increases from 21.01oC to 29.21oC, what is the molar heat of combustion for propane in kJ/mol?

 

11.    Calculate the enthalpy change for the reaction:  2CH4 (g)  +  O2 (g) à  2 CH3OH (l) using the following information:

 

CH4 (g)  +  H2O (g) à  CO (g)  +  3 H2 (g)                     DH = +206.10 kJ

2 H2 (g)  +  CO (g)  à  CH3OH (l)                                   DH = - 128.33 kJ

2 H2 (g)  +  O2 (g) à  2 H2O (g)                                     DH = - 483.64 kJ

 

12.   Write a balanced equation for the fomation of 1 mole of CH3OH (l) from its elements under standard conditions.

 

13.   Using the enthalpies of formation from Appendix C of your book, write a thermochemical equation for the formation of 1 mole of silver nitrate from its elements uder standard conditions.

 

14.   Calculate the enthalpy change for 2 C (s)  +  3 H2 (g) à  C2H6 using the following information:

 

C (s)  +  O2 (g) à CO2 (g)                                                DH = + -393.5 kJ

H2 (g)  +  ½ O2 (g) à  H2O (l)                                         DH =  - 285.8 kJ

2 C2H6 (g)  +  7 O2 (g)  à  4 CO2 (g)  +  6 H2O (l)         DH = -3119.6 kJ

 

15.   Calculate the heat of reaction for the following reaction using the heats of formation given in the appendix of your book.

 

SO2 (g)  +  2 H2S (g) à  3/8 S8 (g)  +  2 H2O (g)

 

16.   Calculate the standard heat of formation for benzene (C6H6) using the following thermochemical equation and the heats of formation given in the appendix of your book.

 

2 C6H6 (l)  +  15 O2 (g) à 12 CO2 (g)  +  6 H2O (l)        DH = -6534 kJ

 

17.   Write the correct formula for:

 

a.   sodium bicarbonate

b.   sulfuric acid

c.   phosphoric acid

d.   calcium nitrate

e.   aluminum sulfate

f.   magnesium hydroxide