Unit 3 Lesson 11: Total Potential Energy
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1. bond energy
the energy required to break chemical bonds
chemical potential energy
the energy stored in bonds
. An example of a molecule with a very strong bond energy is nitrogen gas.
he two nitrogen atoms are held together by a triple bond that is very difficult to break. We can say that this molecule has a very high bond energy.
Two molecules that have very low bond energies are fluorine and iodine, F−F and I−I .
These two molecules easily separate into individual atoms to react with other molecules.
Do atoms have a stronger bond energy when they are closer together or farther apart in a molecule?
Atoms that are closer together have a stronger bond energy.
Define chemical potential energy.
The energy stored in bonds.
The bond energy in an H−H bond is nearly triple the bond energy of an I−I bond. Suggest a reason for this.
The iodine atoms in an I−I bond are much farther apart from each other than the hydrogen atoms are.
Which molecule would have a higher total bond energy, CH4 or NH3 ? Explain how you know and show the calculation.
4×C−H=4×413=1652 kJ/mol 3×N−H=3×391=1173 kJ/mol The CH4 molecule has a higher bond energy than the NH3 molecule.
Do the tennis balls model a stronger bond when they are closer together or farther apart?
Holding the tennis balls closer together models a stronger bond.
Is the bond energy higher in a bond that is modeled by the tennis balls being held farther apart or by the tennis balls being held closer together? Explain.
The higher the bond energy is, the stronger the bond is. The closer together the tennis balls are held, the stronger the bond and the higher the bond energy.
Explain how you know that the energy of the products is lower than the energy of reactants in an exothermic reaction.
Because energy is released to the surroundings.
In an endothermic reaction, the reactants have a __________ (higher/lower) total bond energy. This means the relative potential energy of the reactants is _________ (higher/lower) than the relative potential energy of the products. The reaction ________ (absorbs/releases) energy.
In an endothermic reaction, the reactants have a higher (higher/lower) total bond energy. This means the relative potential energy of the reactants is lower (higher/lower) than the relative potential energy of the products. The reaction absorbs (absorbs/releases) energy.
Which is longer, a nitrogen single bond or a nitrogen triple bond? Which one has a higher bond energy?
The single bond is longer than the triple bond. The triple bond has a much higher bond energy.
Which would have a greater total chemical potential energy, nitrogen gas (N2) or oxygen gas (O2) ? (Hint: The nitrogen molecule has a triple bond and the oxygen molecule has a double bond.)
The nitrogen molecule has a greater chemical potential energy stored in its triple bond.
Blake wants to burn three hydrocarbons, each with five carbons in the molecule. One hydrocarbon has only carbon–carbon single bonds. The second molecule has both single and double bonds. The third molecule includes double and triple bonds. Which molecule will require the greatest input of bond energy to reach the activated state? Explain how you know.
The third molecule has the highest bond energies, so it will require the most energy to break those bonds and cause a reaction.