Select the correct option based on statements given below:
Assertion (A): Combustion of all organic compounds is an exothermic reaction.
Reason (R): The enthalpies of all elements in their standard state are zero.
   
1. Both (A) and (R) are True and (R) is the correct explanation of (A).
2. Both (A) and (R) are True but (R) is not the correct explanation of (A).
3. (A) is True but (R) is False.
4. (A) is False but (R) is True.
Subtopic:  Thermochemistry |
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On the basis of thermochemical equations (i), (ii), and (iii), find out which of the algebraic relationships given in options (a) to (d) is correct:

(i) C(graphite) + O2(g) → CO2 (g) ; ∆rH = x kJmol-1
(ii) C(graphite) + \(\frac{1}{2}\)O2(g) → CO(g) ; ∆rH = y kJ mol-1
(iii) CO(g) + \(\frac{1}{2}\)O2(g) → CO2(g); ∆rH = z kJ mol-1

1. z=x+y

2. x=y-z

3. x=y+z

4. y=2z-x

Subtopic:  Thermochemistry |
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The enthalpies of elements in their standard states are taken as zero. The enthalpy of formation of a compound is-

1. Generally negative 2. Always positive
3. Zero 4. Never negative
Subtopic:  Thermochemistry |
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The enthalpy of sublimation of a substance is equal to:

1. Enthalpy of fusion + Enthalpy of vaporization
2. Enthalpy of fusion
3. Enthalpy of vaporization
4. Twice the enthalpy of vaporization

Subtopic:  Thermochemistry |
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