Predict whether each of the following reactions would be exothermic or endothermic.
a. CO(g) --> C(g) + O(g)
b. 2H(g) + O(g) --> H20(g)
c. Na+(g) + Cl-(g) --> NaCl(s)
What is the sign of DH in each of these reactions?
Please explain. I am very confused. Thanks
a. The reaction CO(g) → C(g) + O(g) involves the breaking of a double bond in CO and the formation of two new bonds in C and O. Breaking bonds generally requires energy, while forming bonds releases energy. Since the formation of bonds releases more energy than is required to break the CO bond, this reaction is exothermic. Therefore, ΔH (enthalpy change) for this reaction is negative (ΔH < 0).
b. The reaction 2H(g) + O(g) → H2O(g) involves the breaking of a double bond in O2 and the formation of two new bonds in H2O. Similar to the previous reaction, breaking bonds requires energy while forming bonds releases energy. The formation of the H2O bonds releases more energy than is required to break the O2 bond, so this reaction is also exothermic. Hence, ΔH for this reaction is negative (ΔH < 0).
c. The reaction Na+(g) + Cl-(g) → NaCl(s) involves the formation of an ionic bond between Na+ and Cl-. Ionic bonds are formed by the transfer of electrons from one atom to another, resulting in the release of energy. In this case, the electron transfer results in the formation of NaCl, resulting in the release of energy. Therefore, this reaction is exothermic, and ΔH for this reaction is negative (ΔH < 0).
In summary:
a. Exothermic (ΔH < 0)
b. Exothermic (ΔH < 0)
c. Exothermic (ΔH < 0)
To predict whether a reaction is exothermic or endothermic, we need to consider the change in enthalpy (ΔH) of the reaction.
a. CO(g) → C(g) + O(g):
To determine the sign of ΔH, we need to analyze the bond energies. Breaking a bond requires energy (endothermic), while forming a bond releases energy (exothermic). In this reaction, a carbon-oxygen double bond in CO is broken, which requires energy. At the same time, a carbon-carbon triple bond and an oxygen-oxygen double bond are formed, which releases energy. Overall, the breaking of a bond requires more energy than the formation of new bonds, making this reaction endothermic. Therefore, the sign of ΔH is positive.
b. 2H(g) + O(g) → H2O(g):
Again, we consider the bond energies. In this reaction, two hydrogen-oxygen bonds are formed in H2O, which releases energy. The breaking of an oxygen-oxygen double bond requires energy. Since the formation of new bonds releases more energy than the breaking of bonds, this reaction is exothermic. Therefore, the sign of ΔH is negative.
c. Na+(g) + Cl-(g) → NaCl(s):
In this reaction, a sodium ion (Na+) and a chloride ion (Cl-) combine to form a solid sodium chloride (NaCl) compound. Since energy is being released during the formation of the ionic bond, this reaction is exothermic. Therefore, the sign of ΔH is negative.
In summary:
a. ΔH > 0, indicating an endothermic reaction
b. ΔH < 0, indicating an exothermic reaction
c. ΔH < 0, indicating an exothermic reaction