Define and provide an example of an exothermic chemical reaction:
Define and provide an example of an endothermic chemical reaction:
Of the bonds listed below the weakest bond is _______ and the strongest is ________.
A strong bond is a (stable / unstable) bond
2(H—C ≡ C—H) + 5(O = O) → 4 (O—C—O) + 2 (H—O—H)
839 kJ/mol C ≡ C # of bonds ______ (product / reactant) side Energy:_____
495 kJ/mo O = O # of bonds ______ (product / reactant) side Energy:_____
413 kJ/mo C—H # of bonds ______ (product / reactant) side Energy:_____
358 kJ/mo C—O # of bonds ______ (product / reactant) side Energy:_____
467 kJ/mo H—O # of bonds ______ (product / reactant) side Energy:_____
Add the energies on the reactant side __________ kJ/mol
Add the energies on the product side __________ kJ/mol
This reaction is (exothermic / endothermic)
The reaction (produces / absorbs) __________ kJ when ____ moles of acetylene (C2H2) reacts.
A pile of firewood is more stable as ash and smoke than firewood.
Why does this pile of firewood not immediately release the energy in
Its chemical bonds? (use the word activation energy in your answer)
An exothermic chemical reaction is a reaction that releases energy in the form of heat. It is characterized by a decrease in the overall energy of the system. An example of an exothermic reaction is the combustion of methane: CH4(g) + 2O2(g) → CO2(g) + 2H2O(g) + energy.
An endothermic chemical reaction is a reaction that absorbs energy from its surroundings. It is characterized by an increase in the overall energy of the system. An example of an endothermic reaction is the process of photosynthesis: 6CO2(g) + 6H2O(l) + energy → C6H12O6(aq) + 6O2(g).
The weakest bond is C—H and the strongest bond is C ≡ C. A strong bond is a stable bond.
Using the given values:
C ≡ C: # of bonds = 2, energy: 839 kJ/mol
O = O: # of bonds = 5, energy: 495 kJ/mol
C—H: # of bonds = 2, energy: 413 kJ/mol
C—O: # of bonds = 4, energy: 358 kJ/mol
H—O: # of bonds = 2, energy: 467 kJ/mol
Adding the energies on the reactant side: 2(839) + 5(495) + 2(413) = 4180 kJ/mol
Adding the energies on the product side: 4(358) + 2(467) = 2712 kJ/mol
This reaction is exothermic.
The reaction produces 4180 - 2712 = 1468 kJ when 1 mole of acetylene (C2H2) reacts.
A pile of firewood does not immediately release the energy in its chemical bonds because it requires an activation energy to initiate the reaction. Activation energy is the minimum amount of energy required for a reaction to occur. In the case of combustion, the firewood needs to be exposed to a flame or intense heat source to provide the activation energy necessary for the reaction to start.