1. When 15.00g of NH3 reacts with excess ClF3, the heat of the reaction is measu

Question

1. When 15.00g of NH3 reacts with excess ClF3, the heat of the reaction is measured to be -24.8 kJ. What is the
?Hrxn for: 2 ClF3 + 2 NH3 ? N2 + 6 HF + Cl2? (1) -3.31 kJ (2) -4.96 kJ (3) -7.29 kJ (4) -56.3 kJ (5) -169 kJ

The answer is 4 but I can't seem to find out to to get it with only that information given.

2. Which of the following compounds has the lowest bond energy? (1) NaCl (2) MgO (3) N2 (4) O2 (5) F2

The answer is 5 but I don't get it. I thought smaller atoms means smaller bond lengths between each other, and since F2 is the smallest shouldn't it be the highest bond energy not the smallest?

Any help is appreciated

Explanation / Answer

Question 1

15 g NH3 is (15/17.031)= .881 mol NH3

Since 2 mol of NH3 are consumed in the reaction, we multiply the heat of reaction by 2, then we adjust for the number of moles we have. The heat of reaction is really saying, -24.8 kilojoules/every mol of product formed. So the calculation looks like this:

(-24.8 kilojoules/mol product)(2 mol NH3/moles product)(15 g/ 17.031 g/mol)= -56.3 kJ

Question 2

The bond energy trend for the periodic table is the same as the atomic radius trend. The fluorine atom is so small and each one has three lone pairs. Since both atoms have three lone pairs, these lone pair electrons are in tight quarters with the bonded electrons, causing stress on the bond that weakens it.

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