Which statement about Kc is wrong?
A. Kc is always a constant
B. For some reactions, Kc increases with temperature increase
C. For some reactions, Kc decreases with temperature decrease
D. For some reactions, Kc changes when pressure is changed
A is incorrect. Kc stays constant for concentration and pressure changes but not for temperature changes.
B and C are correct.
D is incorrect. It is true that a system at equilibrium may be made to shift one way or another (for some reactions) by changing the pressure, BUT, Kc will not change.
I note that the question asks which statement (not statements) are wrong.
To determine which statement about Kc is wrong, let's analyze each option:
A. Kc is always a constant: This statement is incorrect. Kc actually changes with temperature for many reactions. When the temperature is changed, the equilibrium position shifts and this affects the value of Kc.
B. For some reactions, Kc increases with temperature increase: This statement is correct. Increasing the temperature can cause some reactions to shift towards the products, resulting in an increase in the value of Kc.
C. For some reactions, Kc decreases with temperature decrease: This statement is also correct. Decreasing the temperature can cause some reactions to shift towards the reactants, leading to a decrease in the value of Kc.
D. For some reactions, Kc changes when pressure is changed: This statement is incorrect. While changing the pressure can indeed shift the equilibrium position of a reaction, it does not change the value of Kc. Kc only depends on temperature and is unaffected by changes in pressure.
Therefore, the incorrect statement about Kc is A. Kc is always a constant.