Q: If the bond energy of H-F is $$567\ \text{kJ/mol}$$ and that of F-F is $$155\ \text{kJ/mol}$$, what is the energy required to break all bonds in $$2HF$$ and $$Cl_2 in $$the reaction $$2HF(g) + Cl_2$(g) \rightarrow 2HCl(g) + F_2$(g)$$?

$$2 \times 567 + 242 = 1376\ \text{kJ/mol}$$

Q: A student calculates $$\Delta H^\circ$$ for the reaction $$2HF(g) + Cl_2$(g) \rightarrow 2HCl(g) + F_2$(g)$$ using bond energies. Which formula should they use?

$$\Delta H^\circ = \text{(bonds formed)} - \text{(bonds broken)}$$

Question 1

Which of the following correctly arranges Br-Br, Cl-Cl, and I-I in order of increasing bond strength (weakest \u003c strongest) and increasing bond length (shortest \u003c longest) based on periodic trends among group 7A diatomic halogen molecules?

Accepted Answer

I-I \u003c Br-Br \u003c Cl-Cl (bond strength); Cl-Cl \u003c Br-Br \u003c I-I (bond length)

Question 2

Given the following reaction: $$2HF(g) + Cl_2$(g) \rightarrow 2HCl(g) + F_2$(g)$$, and the bond energies: H-Cl = 431 kJ/mol, F-F = 155 kJ/mol, H-F = 567 kJ/mol, Cl-Cl = 242 kJ/mol, what is the estimated $$\Delta H^\circ$$ for the reaction?

Accepted Answer

$$-223\ 	ext{kJ/mol}$$

Question 3

Which statement best explains why the bond strength of I-I is weaker than that of Cl-Cl?

Accepted Answer

Iodine atoms are larger, resulting in a longer bond and less effective orbital overlap.

Question 4

If the bond energy of H-F is $$567\ 	ext{kJ/mol}$$ and that of F-F is $$155\ 	ext{kJ/mol}$$, what is the energy required to break all bonds in $$2HF$$ and $$Cl_2 in $$the reaction $$2HF(g) + Cl_2$(g) ightarrow 2HCl(g) + F_2$(g)$$?

Accepted Answer

$$2 	imes 567 + 242 = 1376\ 	ext{kJ/mol}$$

Question 5

Which of the following is the correct order of bond length for the diatomic halogens Br-Br, Cl-Cl, and I-I?

Accepted Answer

Cl-Cl \u003c Br-Br \u003c I-I

Question 6

A chemist wants to synthesize HCl(g) from HF(g) and Cl2(g). If the bond energies are H-Cl = $$431\ 	ext{kJ/mol}$$, H-F = $$567\ 	ext{kJ/mol}$$, Cl-Cl = $$242\ 	ext{kJ/mol}$$, and F-F = $$155\ 	ext{kJ/mol}$$, which bonds are broken and which are formed in the reaction $$2HF(g) + Cl_2$(g) ightarrow 2HCl(g) + F_2$(g)$$?

Accepted Answer

Broken: H-F and Cl-Cl; Formed: H-Cl and F-F

Question 7

Which of the following best describes the relationship between bond length and bond strength in diatomic halogen molecules?

Accepted Answer

As bond length increases, bond strength decreases.

Question 8

If the bond energy of Cl-Cl is $$242\ 	ext{kJ/mol}$$ and that of F-F is $$155\ 	ext{kJ/mol}$$, which bond is easier to break and why?

Accepted Answer

F-F is easier to break because it has a lower bond energy.

Question 9

A student calculates $$\Delta H^\circ$$ for the reaction $$2HF(g) + Cl_2$(g) \rightarrow 2HCl(g) + F_2$(g)$$ using bond energies. Which formula should they use?

Accepted Answer

$$\Delta H^\circ = 	ext{(bonds formed)} - 	ext{(bonds broken)}$$

Question 10

Which of the following is a plausible reason why the bond energy of H-F is much higher than that of F-F?

Accepted Answer

H-F bond is highly polar, leading to stronger attraction between atoms.

Question 11

If a reaction involves breaking two H-F bonds and one Cl-Cl bond, and forming two H-Cl bonds and one F-F bond, what is the net energy change ($$\Delta H^\circ) $$using the following bond energies: H-F = $$567\ 	ext{kJ/mol}$$, Cl-Cl = $$242\ 	ext{kJ/mol}$$, H-Cl = $$431\ 	ext{kJ/mol}$$, F-F = $$155\ 	ext{kJ/mol}$$?

Accepted Answer

$$-223\ 	ext{kJ/mol}$$

Question 12

Which halogen molecule would you expect to have the shortest bond length?

Accepted Answer

Cl-Cl

Question 13

Why is the bond energy of Cl-Cl lower than that of H-F?

Accepted Answer

Cl-Cl bond is nonpolar and has less effective orbital overlap compared to H-F.

Question 14

Which of the following best describes the trend in bond strength among the halogen molecules as you move down the group?

Accepted Answer

Bond strength decreases as atomic size increases.

Question 15

If you were to estimate the enthalpy change for a reaction using bond energies, which step would you perform first?

Accepted Answer

Identify which bonds are broken and which are formed.

Periodic Trends and Bond Energies in Halogen Chemistry

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