Consider the gas-phase reaction of ethylene (CH 2 CH 2) with hydrogen to form ethane (C 2H 6), which occurs in the presence of a palladium catalyst (Section 6.4B). a. Write the expression for the equilibrium constant for this reaction. b. If ΔH = −28 kcal/mol, are the products or reactants higher in energy? c. Which is likely to be true about the equilibrium constant for the reaction: K > 1 or K < 1? d. How much energy is released when 20.0 g of ethylene reacts? e. What happens to the rate of the reaction if the concentration of ethylene is increased? f. What happens to the equilibrium when each of the following changes occurs: [1] an increase in [H 2]; [2] a decrease in [C 2H 6]; [3] an increase in temperature; [4] an increase in pressure; [5] removal of the palladium catalyst?
Thermochemistry
Thermochemistry can be considered as a branch of thermodynamics that deals with the connections between warmth, work, and various types of energy, formed because of different synthetic and actual cycles. Thermochemistry describes the energy changes that occur as a result of reactions or chemical changes in a substance.
Exergonic Reaction
The term exergonic is derived from the Greek word in which ‘ergon’ means work and exergonic means ‘work outside’. Exergonic reactions releases work energy. Exergonic reactions are different from exothermic reactions, the one that releases only heat energy during the course of the reaction. So, exothermic reaction is one type of exergonic reaction. Exergonic reaction releases work energy in different forms like heat, light or sound. For example, a glow stick releases light making that an exergonic reaction and not an exothermic reaction since no heat is released. Even endothermic reactions at very high temperature are exergonic.
Consider the gas-phase reaction of ethylene (CH 2 CH 2)
with hydrogen to form ethane (C 2H 6), which occurs in the
presence of a palladium catalyst (Section 6.4B).
a. Write the expression for the equilibrium constant for this
reaction.
b. If ΔH = −28 kcal/mol, are the products or reactants
higher in energy?
c. Which is likely to be true about the equilibrium constant
for the reaction: K > 1 or K < 1?
d. How much energy is released when 20.0 g of ethylene
reacts?
e. What happens to the
f. What happens to the equilibrium when each of the following changes occurs: [1] an increase in [H 2]; [2] a decrease
in [C 2H 6]; [3] an increase in temperature; [4] an increase in
pressure; [5] removal of the palladium catalyst?
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