The values of ∆H for endothermic and exothermic reactions are

positive and negative

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negative for both

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negative and positive

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positive for both

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Solution

The correct option is A
positive and negative

In exothermic reactions heat is given out so the enthalpy of products is less than the enthalpy of the reactants and the enthalpy change is negative. In endothermic reactions, heat is absorbed this increases the enthalpy of the products in such a case enthalpy change of the reaction is positive.

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Similar questions

Q. Assertion :

Δ H

for an exothermic reaction is negative and for an endothermic reaction is positive. Reason: Enthalpy is an extensive property.

	Column I		Column II
a.	exothermic	p.	$H_{P} - H_{R}$
b.	endothermic	q.	$Δ H$ is negative
c.	spontaneous	r.	$Δ H$ is positive
d.	heat of reaction	s.	$Δ G$ is negative

In an exothermic reaction, heat is evolved, and system loses heat to the surrounding. For such system
(a) $q_{p}$ will be negative
(b) $Δ_{r} H$ will be negative
(c) $q_{p}$ will be positive
(d) $Δ_{r} H$ will be positive

Q. Predict whether the reaction

C O (g) + (\frac{1}{2}) O_{2} (g) \to C O_{2} (g)

at 300 K is spontaneous & exothermic or non-spontaneous & endothermic, when the standard entropy change is

- 0.094 k J m o l^{- 1} K^{- 1} .

The standard Gibb's free energies of formation for

C O_{2}

and

C O

are

- 394.4 a n d - 137.2 k J m o l^{- 1}

respectively.

For the reaction Hg ---------> Hg (), the entropy change will have the sign:

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