Question 1

Which atoms are present in boranes, such as diborane ($\mathrm{B_2H_6}$)?

Accepted Answer

Boron and hydrogen

Question 2

In diborane ($\mathrm{B_2H_6}$), what type of bonds connect the two boron atoms?

Accepted Answer

Bridged hydrogen bonds

Question 3

What is the hybridization of the boron atoms in diborane ($\mathrm{B_2H_6}$)?

Accepted Answer

$sp^3$

Question 4

Which of the following best describes the bonding in diborane ($\mathrm{B_2H_6}$)?

Accepted Answer

There are two three-center two-electron bonds involving boron and hydrogen.

Question 5

Given the following reaction: $2\mathrm{B} + 3\mathrm{H}_2 \rightarrow \mathrm{B}_2\mathrm{H}_6$, which of the following is the correct enthalpy change ($\Delta H$) for the formation of diborane from its elements, using the provided enthalpy values?

Accepted Answer

$-36\ \mathrm{kJ}$

Question 6

Which statement about the hydrogen atoms in diborane ($\mathrm{B_2H_6}$) is correct?

Accepted Answer

Four hydrogen atoms are terminal, and two are bridging between boron atoms.

Question 7

Which of the following best explains why diborane ($\mathrm{B_2H_6}$) does not follow the octet rule for boron?

Accepted Answer

Boron atoms in diborane have less than eight electrons due to three-center two-electron bonds.

Question 8

If the enthalpy of formation for $\mathrm{B_2O_3}$ is $-1273\ \mathrm{kJ}$ and for $\mathrm{H_2O}$ is $-286\ \mathrm{kJ}$, what is the enthalpy change for the reaction $2\mathrm{B} + 3\mathrm{H}_2 + 3\mathrm{O}_2 \rightarrow \mathrm{B_2O_3} + 3\mathrm{H_2O}$?

Accepted Answer

$-2145\ \mathrm{kJ}$

Question 9

Which of the following is a correct description of a three-center two-electron bond?

Accepted Answer

A bond where three atoms share two electrons.

Question 10

In the context of boranes, what is the significance of the bridging hydrogen atoms?

Accepted Answer

They participate in three-center two-electron bonds, stabilizing the molecule.

Question 11

Which of the following is NOT a property of diborane ($\mathrm{B_2H_6}$)?

Accepted Answer

It has a direct boron-boron single covalent bond.

Question 12

A chemist wants to synthesize diborane ($\mathrm{B_2H_6}$) in the laboratory. Which reactants should be used according to the formation reaction?

Accepted Answer

$2\mathrm{B} + 3\mathrm{H}_2$

Question 13

Which of the following statements about the structure of diborane ($\mathrm{B_2H_6}$) is correct?

Accepted Answer

It has a non-planar structure due to the bridging hydrogens.

Question 14

If the enthalpy of formation for $\mathrm{NH_3}$ is $-46\ \mathrm{kJ}$, what is the enthalpy change for the reaction $N_2 + 3H_2 \rightarrow 2NH_3$?

Accepted Answer

$-92\ \mathrm{kJ}$

Question 15

Which of the following best describes the difference between terminal and bridging hydrogen atoms in diborane ($\mathrm{B_2H_6}$)?

Accepted Answer

Terminal hydrogens are bonded to one boron atom, while bridging hydrogens are bonded to two.

Question 16

Which of the following is a consequence of the electron deficiency in diborane ($\mathrm{B_2H_6}$)?

Accepted Answer

It forms three-center two-electron bonds.

Question 17

Which of the following reactions represents the formation of water from its elements?

Accepted Answer

$2H_2 + O_2 \rightarrow 2H_2O$

Question 18

Which of the following is the correct Lewis structure for diborane ($\mathrm{B_2H_6}$)?

Accepted Answer

Each boron atom is bonded to two terminal hydrogens and shares two bridging hydrogens with the other boron atom.

Boranes: Structure, Bonding, and Thermochemistry

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