Which of the following reactions is endothermic?

h2(g) + ½o2(g) → h2o(g), δh = -57.82 kcal
½n2(g) + o2(g) + 8.1 kcal → no2(g)
½n2(g) + 3/2h2(g) → nh3(g) + 11.0 kcal
c(diamond) + o2(g) → co2, δh = -94.50 kcal

Explanation:

Chemical reaction

When two or more substances react and form some new substance it is called as chemical reaction .

A + B --> C + D

(reactants )   (products )

When ever chemical reaction occurs following changes can occur :

On the basis of energy changes : reactions are of two types :

Endothermic

Exothermic

Endothermic reaction

A reaction in which heat is absorbed .

Example :½N2(g) + O2(g) + 8.1 kcal → NO2(g)

Exothermic reaction

A reaction in which heat is released .

For example : H2(g) + ½O2(g) → H2O(g), ΔH = -57.82 kcal

½N2(g) + 3/2H2(g) → NH3(g) + 11.0 kcal

C(diamond) + O2(g) → CO2, ΔH = -94.50 kcal