Reaction and Bond Enthalpy

When new chemical bonds form, energy ____________.

• is taken into the system.

• is released from the system.

• stays the same in the system.

Does breaking bonds require energy, release energy, or not involve energy at all?

• requires energy to break

• releases energy when broken

• No energy involved

Use bond energies to determine the energy change for the following reaction and use the information to determine if it is an endothermic or exothermic reaction:

HCN + H₂ --> CH₃N₂

Bond enthalpy is __________.

• always negative

• always positive

• sometimes positive and sometimes negative

• always zero

• unpredictable

As the number of covalent bonds between two atoms increases, the distance between the atoms ______ and the strength of the bond between them ______.

• increases, increases

• decreases, decreases

• increases, decreases

• decreases, increases

• is unpredictable

The ion NO- has _____ valence electrons.

• 10

• 12

• 14

• 15

• 16

Is this equation endo- or exo-thermic?

2KNO₃ (s) + energy --> 2KNO₂ (s) + O₂

• endothermic

• exothermic

What is the overall reaction enthalpy for the following reaction:

4 NH3 + 7 O2 --> 4 NO2 + 6 H2O

delta H NH3: -46 kJ/mol

deltaH O2: 0 kJ/mol

deltaH NO2: 34 kJ/mol

deltaH H2O: -286 kJ/mol

• 206 kJ/mol

• -206 kJ/mol

• 1396 kJ/mol

• -1396 kJ/mol