In the reactions
(I) H2 (g) + 1/2O2(g) → H2O(l); ∆H = -286 KJ
(II) C(s) + O2g) → CO2 (g); ∆H = -406 KJ the equations imply that
more heat is absorbed in (l)
more heat is absorbed in (ll)
less heat is evolved in (l)
reaction (ll) proceeds faster than (l)
reaction (l) proceeds faster than (ll)
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Discussions (18)
The answer is C.
Heat is not absorbed in an exothermic reaction, it is released. So the answer can never be A or B.
Option C: Less heat is evolved in (I) compared to (II) because -286 KJ is less than -406 KJ.
Option D & E: The speed of a reaction depends on factors like activation energy and catalysts, not just the enthalpy change. The question does not provide information on kinetics, so these options cannot be confirmed.
The correct answer is D. reaction (II) proceeds faster than (I).
The more negative the ∆H value, the more exothermic (heat-releasing) the reaction is, and the faster it proceeds. Since reaction (II) has a more negative ∆H value (-406 kJ) compared to reaction (I) (-286 kJ), reaction (II) proceeds faster than reaction (I).
Here's a brief explanation of the other options:
A. More heat is absorbed in (I): This is incorrect, as the negative ∆H value indicates heat is evolved, not absorbed.
B. More heat is absorbed in (II): This is also incorrect, as the negative ∆H value indicates heat is evolved, not absorbed.
C. Less heat is evolved in (I): This is incorrect, as reaction (I) does evolve heat, just less than reaction (II).
E. Reaction (I) proceeds faster than (II): This is the opposite of the correct answer, as reaction (II) proceeds faster due to its more negative ∆H value.
The answer shouldn't be C, but if it is, then Myschool should please explain why.
-286 is greater than -406, so for reaction (I), the heat evolved is greater than the heat evolved in reaction (ii) and seeing that it's an exothermic reaction, reaction (I) should proceed faster than reaction (ii) because more heat is evolved in reaction (I)
I think since -286 is greater than -406 it means eq(I) is more exothermic and (ii) is exothermic but less than (I)
therefore more heat is liberated in (I) and less is absorbed
and more heat is liberated also in ii)
-ve means it is an exothermic and heat is been released to the atmosphere
while +ve means it is an endothermic reaction meaning heat is been absolved
so therefore since (i) released -286kj of energy and (ii) released -406kj
Then we say (i) released less amount of heat
and (ii) released more
The ∆H values given in the reactions represent the change in enthalpy, which is the heat absorbed or released in a reaction at constant pressure. A negative ∆H value indicates that the reaction is exothermic, meaning it releases heat.
In reaction (I), the ∆H value is -286 KJ, indicating that 286 KJ of heat is released.
In reaction (II), the ∆H value is -406 KJ, indicating that 406 KJ of heat is released.
Therefore, more heat is released (or evolved) in reaction (II) than in reaction (I). So, the correct answer is **B. more heat is absorbed in (II)**.
