Thermochemistry Review Questions (Chemistry 30)

Thermochemistry Review Questions (Chemistry 30)

1. How much heat is required to raise the temperature of 7.35g of water from 21.0°C to 98.0°C?

1. How much heat in kJ is required to raise the temperature of 8.00 ounces of water (237g) from 4.0°C to body temperature?

1. How much heat in kJ is required to raise the temperature of 2.50g Hg(l) from -2.00°C to 6.00°C. Assume the density of Hg is 13.6g/mL and a molar heat capacity of 28.0J/mol°C.

1. When 1.0kg of lead (specific heat capacity 0.160J/g°C) at 100.0°C is added to a quantity of water at 28.5°C, the final temperature of the lead water mixture is 35.2°C. What is the mass of water present?

1. A 1.00g copper sample at 100.0°C is added to 50.0g water at 26.5°C. What is the final temperature of the copper water mixture?

1. Vanillin is a natural constituent of vanilla. It is also manufactured for use in artificial vanilla flavoring. The combustion of 1.013g of vanillin C8H8O3 in a calorimeter causes 1.17kg of water to heat from 24.89°C to 30.09°C. What is the molar heat of combustion of vanillin?

1. The combustion of a 1.176g sample of benzoic acid causes a temperature increase of 4.96°C in a calorimeter containing 1000g of an unknown liquid (not aqueous solution). The heat of combustion of benzoic acid is

-3226kJ/mol. Determine the heat capacity of the liquid in the calorimeter.

1. Two solutions, 100.0mL of 1.00mol/L AgNO3(aq) and 100.0mL of 1.00mol/L NaCl(aq) both initially 22.4°C are added to a Styrofoam cup calorimeter and allowed to react. The temperature rises to 30.2°C. Determine the molar enthalpy of the reaction.

1. Two solutions, 100.0mL of 1.020mol/L HCl and 50.0mL of 1.988mol/L NaOH, both initially 24.52°C are mixed in a Styrofoam cup calorimeter. Determine the molar enthalpy of neutralization if the final temperature of the mixture is 33.69°C.

1. What mass of sucrose must be burned to produce 1.00x103kJ of heat?

1. A 25.0mL sample of 0.1045mol/L HCl(g) was neutralized by NaOH(aq). Determine the heat evolved in this neutralization reaction (assume solid and liquid products are only produced)

1. The enthalpy of formation for the amino acid leucine C6H13O2N(s) is -637.3kJ/mol. Write the chemical equation to which this value applies. Using this, determine your chemical reaction using only whole number coefficients.

1. Calculate the heat of combustion per mole of a gaseous fuel that contains C3H8(g) and C4H10(g).

1. Determine the heat of formation of benzene for the following reaction:

2C6H6(l) + 15O2(g)  12CO2(g) + 6H2O(l) ΔH = -6.535x103kJ

1. What is the enthalpy change for the reaction of magnesium chloride and sodium hydroxide?

1. Use Hess’s law to determine ΔH for the reaction C3H4(g) + 2H2(g)  C3H8(g) given that

H2(g) + ½ O2(g)  H2O(l)

C3H4(g) + 4O2(g)  3CO3(g) + 2H2O(l) ΔH = -1937kJ

C3H8(l) + 5O2(g)  3CO3(g) + 4H2O(l) ΔH = -2219.1kJ

Electrochemistry Review Questions (Chemistry 30)

1. Write the net equation for the redox reaction that occurs in a Scandium Silver voltaic cell (assuming the Scandium Electrode Potential to be -2.02V)

1. Draw a silver aluminum voltaic cell. Label the cathode, anode and all other features of the cell. Write the relevant equations under your cell and calculate the cell potential.

1. What is the cell potential for the reaction of FeCl2(aq) with Cl2(g)

1. Predict the products when Pt electrodes are used in the electrolysis of KI(aq)

1. In the electrolysis of AgNO3(aq) what are the expected products if the anode is silver and the cathode is platinum?

1. If 12.3g of Cu is deposited at the cathode of an electrolytic cell after 5.50h what was the current used?

1. For how long would the electrolysis of copper sulfate have to be carried out using Pt electrodes and a current of 2.13A to produce 2.62L of oxygen gas at 26.2°C and 738mmHg pressure at the anode?

(R = 8.314LkPa/molK = 62.364LmmHg/molK)

1. Write the half reactions and the net equation for the following reaction. Label the oxidizing agent / reducing agent, reduction and oxidation half reactions, and calculate the cell potential. Finally, determine whether the reaction is spontaneous or non-spontaneous.

1. CuSO4(aq) + Fe(s)
2. NaBr + Cl2(g)
3. NaCl + Br2(g)
4. Fe2(SO4)3(aq) + Al

1. Compare and contrast corrosion of iron caused under atmospheric conditions, compared with corrosion under acid rain conditions. Use half reactions in your discussion and list 3 chemical solutions to the problem of corrosion

Thermochemistry Review KEY

1. Q = 2.371kJ
2. Q = 32.77kJ
3. omit…. This question is too in depth for chem 30 (sorry!)
4. m = 369.32g
5. tf = 26.6348°C
6. ΔHm =-3829.0786kJ/mol
7. c = 6.26kJ/kg°C
8. ΔHm =-6.5364kJ/mol
9. ΔHm =-57.98kJ/mol
10. m = 66.4g sucrose
11. ΔH = Q =0.275kJ
12. 6C + 13/2H2 + 1O2 + 1/2N2 C6H13O2N + 637.3kJ
13. ΔHcombustion C3H8 = -2043.9kJ/mol, ΔHcombustion C4H10 = -2657.3kJ/mol
14. ΔHmf = 49.1kJ/mol
15. ΔHrxn = -254kJ
16. ΔHrxn =-289.5kJ

Electrochemistry Review KEY

1. 3Ag+(aq) + Sc(s)  3Ag(s) + Sc3+(aq)
2. Anode – Oxidation

Al(s)  Al3+(aq) + 3e-

Cathode + Reduction

Ag1+(aq) + 1e-  Ag(s)

1. E°cell = 0.59V
2.  I2(g) + H2(g) + 2OH-(aq)
3.  Silver will plate the platinum electrode
4. I = 1.886A
5. t = 5.214hours
6. a. Fe(s) + Cu2+(aq)  Fe2+(aq) + Cu(s) = SPONTANEOUS E°cell = 0.79V

b. Cl2(g) + 2Br1-(aq)  2Cl1-(aq) + Br2(g) = SPOTANEOUS E°cell = 0.29V

c. 2Cl1-(aq) + Br2(g)  Cl2(g) + 2Br1-(aq) = NONSPONT E°cell = -0.29V

d. 3Fe3+(aq) + 1Al(s)  3Fe2+(aq) + 1Al3+(aq) = SPONTANEOUS E°cell = 2.43V

1. 2Fe(s) + 2H2O(l) + O2(g)  2Fe2+(aq) + 4OH-(aq) regular rusting

2Fe(s) + O2(g) + 4H+(aq)  2Fe2+(aq) + 2H2O(l) acid rusting increases spont

Sacrificial Anode – oxidizes instead of the metal (Fe) bc it’s a stronger RA

Galvanization – coats the metal so nothing can get at it AND is a stronger RA

Painting – coats metal so water, oxygen and acid cannot reach metal

Alloys – mixing a metal with another (i.e. stainless steel)