Determine whether the following are endothermic or exothermic.
2H2O2 (l) �¨ 2H2O(l) + O2(g)
∆H = -190 kj
C(s) + H2O (g) �¨ CO (g) + H2 (g)
∆H = +113 kj
C4H9OH(l) + 6 O2(g) �¨ 4 CO2(g) + 5 H 2O(g)
∆H = -2456.1
2 C(s) + H2(g) �¨ C2H2(g)
∆H = +226.71
N2O5(s) + H2O(l) �¨ 2 HNO3(aq)
∆H = -86.0
thanks!
The endothermic reactions have negative ∆H values, because, for thosue reactions, chemical energy is lost when heats of formation of reactants and products are compared at the same temperature.
To determine whether a reaction is endothermic or exothermic, we need to look at the sign of the ∆H (change in enthalpy) value.
1. 2H2O2(l) → 2H2O(l) + O2(g) (∆H = -190 kJ)
This reaction has a ∆H value of -190 kJ. Since the ∆H value is negative, it means that the reaction releases heat to the surroundings. Therefore, it is an exothermic reaction.
2. C(s) + H2O(g) → CO(g) + H2(g) (∆H = +113 kJ)
In this reaction, the ∆H value is positive (+113 kJ). A positive ∆H indicates that heat is absorbed from the surroundings. Thus, this reaction is endothermic.
3. C4H9OH(l) + 6 O2(g) → 4 CO2(g) + 5 H2O(g) (∆H = -2456.1 kJ)
The ∆H value for this reaction is -2456.1 kJ, which is negative. This negative value indicates that heat is released to the surroundings, making it an exothermic reaction.
4. 2 C(s) + H2(g) → C2H2(g) (∆H = +226.71 kJ)
The ∆H value for this reaction is +226.71 kJ, which is positive. Therefore, this reaction is endothermic as it absorbs heat from the surroundings.
5. N2O5(s) + H2O(l) → 2 HNO3(aq) (∆H = -86.0 kJ)
In this reaction, the ∆H value is negative (-86.0 kJ), indicating that heat is released to the surroundings. Thus, it is an exothermic reaction.
In summary:
- Exothermic reactions release heat to the surroundings and have negative ∆H values.
- Endothermic reactions absorb heat from the surroundings and have positive ∆H values.