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
I don't know how this got copied three times. Sorry
To predict whether a reaction is exothermic or endothermic, you need to consider the change in enthalpy (ΔH) for each reaction. Enthalpy is a measure of the heat energy involved in a chemical reaction.
a. CO(g) --> C(g) + O(g)
To determine the sign of ΔH, you need to consider the number and types of bonds being broken and formed. In this reaction, a double bond between carbon and oxygen is being broken, and two new bonds (a single bond between carbon and carbon, and a double bond between oxygen atoms) will be formed.
Breaking a bond requires energy to overcome the attraction between the atoms, which is an endothermic process. On the other hand, forming a bond releases energy as the atoms come together and stabilize, which is an exothermic process.
In this reaction, one bond is broken (which is endothermic) and two bonds are formed (which is exothermic). Since the energy released from bond formation is greater than the energy required to break the bond, the overall reaction is exothermic.
Therefore, the sign of ΔH for this reaction is negative (∆H < 0), indicating that it is exothermic.
b. 2H(g) + O(g) --> H2O(g)
In this reaction, two hydrogen atoms react with one oxygen atom to form a water molecule. During this process, one H-H bond and one O=O bond are broken, and two new O-H bonds are formed.
Again, breaking bonds is endothermic, while forming bonds is exothermic.
In this case, two bonds are broken (which is endothermic), and two bonds are formed (which is exothermic). The energy required to break the bonds is equivalent to the energy released during bond formation.
Therefore, the overall reaction neither absorbs nor releases energy. ΔH is close to zero (∆H ≈ 0), indicating that it is neither exothermic nor endothermic.
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 crystal.
Ionic compounds involve the transfer of electrons, rather than the formation or breaking of covalent bonds. Therefore, the concept of bond energy is not applicable here.
When ionic compounds form, oppositely charged ions come together to minimize their electrostatic potential energy. This process releases energy, making the overall reaction exothermic.
Therefore, the sign of ΔH for this reaction is negative (∆H < 0), indicating that it is exothermic.
I hope this explanation helps you understand the concept of bond energies and how they influence the sign of ΔH in chemical reactions.