3. Considering the reaction: 2Fe 2 O 3 + 3C --> 4Fe + 3CO 2 A. How many moles of

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)

Explanation / Answer

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*Kf*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.

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