Question

1) C2H6 (g) -----> C2H4 (g) + H2 (g) ΔH1 = ? 2) C2H6 (g) + 3.5O2 (g) -----> 2CO2 (g) + 3H2O (l) ΔH2 = -1558 kJ/mo 3) C2H4 (g) + 3O2 (g) -----> 2CO2 (g) + 2H2O (l) ΔH3 = -1408 kJ/mol 4) 2H2O (l) -----> 2H2 (g) + O2 (g) ΔH4 = 568 kJ/mol A: Calculate ΔHrxn for reaction (1) based on the given data. Is this reaction endothermic or exothermic? B: How much heat is transferred between the system and the surroundings when 25 grams of ethane (C2H6) decomposes to produce ethylene (C2H4) and hydrogen gas? Is energy is released or absorbed by the system? *** Hint: You will need to calculate ΔH1 and use this value in your calculations to solve for this problem. ***

Answer 1

(A)

Answer :-

1)

2) The reaction is an endothermic reaction because is positive (i.e. + 134 (kJ/mol))

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Explanation :-

Given :-

...(1)

...(2)

...(3)

....(4)

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first Multiply equation (2) by 2

...(5)

next, reverse equation (3) and multiply by 2

Now, add equation (4), (5) and (6)

  

+ +  ---------------------------------------------------------------------------

...(7)

divide equation (7) by 2 we get equation (1)

(since, 1 mole of C2H6 is reacted, enthalpy has unit kJ/mol)

Therefore for reaction (1) is 134 kJ/mol

As (134 kJ) is positive, reaction is endothermic.

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(B)

Answer :-

1) 111.67 kJ heat transfer between system and surrounding.

2) as (111.67 kJ) is positive, heat is absorbed by the system.

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Explanation :-

From part A we have,

..(A)  

i.e. 1 mole of ethane decomposes to produce 1 mole of ethylene and 1 mole hydrogen gas.

Given :- mass of ethane = 25 gram

we know 1 mol of ethane = 30 g ethane

Now we know that from reaction (A)

1 mole ethane decomposes by absorbing 134 kJ heat

i.e. 30 g ethane decomposes by absorbing 134 kJ heat

then 25 g ethane decomposes by absorbing =

=  = 111.67 kJ heat

Therefore,  111.67 kJ heat is transferred between the system and the surroundings when 25 grams of ethane (C2H6) decomposes to produce ethylene (C2H4) and hydrogen gas.  

As (111.67 kJ) is positive, energy is absorbed by the system.

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