JEE MAIN - Chemistry (2020 - 7th January Evening Slot - No. 19)
The standard heat of formation $$\left( {{\Delta _f}H_{298}^0} \right)$$ of ethane (in kj/mol), if the heat of combustion of
ethane, hydrogen and graphite are - 1560, -393.5 and -286 Kj/mol, respectively is :
Answer
-192.5
Explanation
2C(graphite)+ 3H(g) $$ \to $$ C2H6(g)
$${\Delta _f}H$$(C2H6) = 2$$\Delta H$$comb(Cgraphite) + 3$$\Delta H$$comb(H2)
- $$\Delta H$$comb(C2H6)
= – (286$$ \times $$2) - (393.5$$ \times $$3) -(-1560)
= -572 –1180.5+1560 = -192.5 kJ/mole
$${\Delta _f}H$$(C2H6) = 2$$\Delta H$$comb(Cgraphite) + 3$$\Delta H$$comb(H2)
- $$\Delta H$$comb(C2H6)
= – (286$$ \times $$2) - (393.5$$ \times $$3) -(-1560)
= -572 –1180.5+1560 = -192.5 kJ/mole
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