Question

3. Considering the reaction:
2Fe₂O₃ + 3C --> 4Fe + 3CO₂

A. How many moles of C are needed to react with 6.00 moles of Fe₂0₃

B. How many grams of Fe result when 175g of Fe₂O₃ react?

4. Using the bond energies below determine the value and sign of delta H for..
   H-S-H + Cl-Cl --> Cl-S-Cl + H-H

Bond energies in kJ/mol:
H-S 365 Cl-Cl 240 Cl-S 255 H-H 432

5. Will a 1.0m solution of ZnCl₂ in water have the same freezing temperature as..
A. 1.0m solution of NaCl in water? Give a reason for your answer.

7. Al metal has a specific heat of 0.880 J/gram-degree C. How many joules of heat are needed to heat 562g of Al from 25.0 degrees C to 95.0 degrees C?

8. The enthalpy of combustion of C₂H₆ is 1541 kJ/mole. How many kJ of heat results when 775 grams of C₂H₆ are combusted?

9. Explain why although both NaCl and sucrose, C₁₂H₂₂O₁₁, are soluble in water one of their solutions conducts electricity, but the other does not.

10. A sample of a hydrate of NiCl₂ weighing 0.235 grams is heated to drive off the water leaving a weight of 0.128 grams. What is the formula for the hydrate? i.e What is the value of X in NiCl₂(XH₂0)

Answer 1

3) 2Fe₂O₃ + 3C --> 4Fe + 3CO₂

Fe₂O₃ & C reacts in the molar ratio of 2:3

Thus, for 6 moles of Fe₂O₃ , moles of C required = (3*6/2) = 9 moles

Now, molar mass of Fe₂O₃ = 160 g/mole

Thus, moles of Fe₂O₃ in 175 g of it = mass/molar mass = 175/160 = 1.094

Now, 2 moles of Fe₂O₃ produces 4 moles of Fe

Thus, 1.094 moles of Fe₂O₃ produces 2.1875 moles of Fe

Molar mass of Fe = 56 g/mole

Thus, mass of Fe produced = moles*molar mass = 122.5 g

5) ZnCl₂(aq) ---------> Zn²⁺(aq) + 2Cl^-(aq)

Van't Hoff's factor,i = 3

NaCl(aq) -------> Na⁺(aq) + Cl^-(aq)

Van't Hoff's factor,i = 2

depression in F.P = i*K_f*m

thus, F.P of the two solutions will not be the same

7) Heat gain/loss = mass*specific heat*change in temperature

or, Heat gained = 562*0.88**70 = 34619.2 J = 34.6192 kJ

8) molar mass of C₂H₆ = 30 g/mole

Thus, moles of C₂H₆ in 775 g of it = mass/molar mass = 25.834

Hence heat produced = 25.834*1541 = 39809.2 kJ

9) NaCl & sucrose both are soluble in water but NaCl dissociates into ions in water which conducts electricity while sucrose doesnot dissociates and hence doesnot conduct electricity.