The dependence of the equilibrium constant of a reaction on temperature is given by the van't Hoff equation:
where C is a constant. The following table gives the equilibrium constant
KP |
138 |
5.12 |
0.436 |
0.0626 |
0.0130 |
TOO |
600 |
700 |
800 |
900 |
1000 |
(a) Determine graphically the
How does this equation support the prediction based on Le Châ�telier's principle about the shift in equilibrium with temperature? (c) The vapor pressures of water are 31.82 mmHg at
Interpretation:
The
Concept Introduction:
Achemical equilibrium is a state of the chemical reaction when the rate of forward reaction becomes equal to the rate of reverse reaction and the concentrations of the products and reactants become constant, which are known as equilibrium concentrations.
When energy is released in a reaction, the reaction is called exothermic, and the reactions in which energy is absorbed are endothermic reactions.
According to Le Chatelier’s Principle, when a system at equilibrium is subjected to any change, the system tries to undo the effect of that change by shifting its equilibrium in the desired direction.
The van't Hoff equation provides information about the temperature dependence of the equilibrium constant.
Answer to Problem 125AP
Solution:
(a)
(b)
According to Le Chatelier’s principles, increase in temperature favors the forward endothermic reaction, and decrease in temperature favors an exothermic reaction.
(c)
Explanation of Solution
a)The
The
The slope of the plot is
Here,
Substitute the values of
The
b)The following equation support the prediction based on Le-Chatelier’s principle about the shift in equilibrium with temperature
The vant Hoff’s equation at two different temperatures is
Here,
From (1) and (2):
An endothermic reaction has
Then, temperature is
In a reversible reaction at equilibrium, when the equilibrium constant is more, the products are also more or the rate constant of forward reaction is more, and hence the products are more. According to LeChatelier’s principle, an increase in temperature favors endothermic reaction, and a decrease in temperature favors exothermic reaction.
c) Molar heat of vaporization of water
The vapor pressure of water is
From vant’s Hoff equation,
Here,
Substitute the values of
On further solving
The molar heat ofvaporization of water is
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Chapter 15 Solutions
Chemistry
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