Consider the following system at equilibrium where H° = -111 kJ, and Kc = 0.159
ID: 1001543 • Letter: C
Question
Consider the following system at equilibrium where H° = -111 kJ, and Kc = 0.159 , at 723 K: N2 (g) + 3 H2 (g) 2 NH3 (g)
If the TEMPERATURE on the equilibrium system is suddenly decreased :
The value of Kc A. Increases B. Decreases C. Remains the same
The value of Qc A. Is greater than Kc B. Is equal to Kc C. Is less than Kc
The reaction must: A. Run in the forward direction to restablish equilibrium. B. Run in the reverse direction to restablish equilibrium. C. Remain the same. Already at equilibrium.
The concentration of H2 will: A. Increase. B. Decrease. C. Remain the same.
Consider the following system at equilibrium where H° = 16.1 kJ, and Kc = 6.50×10-3, at 298 K: 2NOBr(g) 2NO(g) + Br2(g)
If the TEMPERATURE on the equilibrium system is suddenly increased:
The value of Kc A. Increases B. Decreases C. Remains the same
The value of Qc A. Is greater than Kc B. Is equal to Kc C. Is less than Kc
The reaction must: A. Run in the forward direction to restablish equilibrium. B. Run in the reverse direction to restablish equilibrium. C. Remain the same. Already at equilibrium.
The concentration of Br2 will: A. Increase. B. Decrease. C. Remain the same.
Explanation / Answer
Part 1:
This reaction is exothermical because the value of the enthalpy is negative, this means that you need to REMOVE heat to favor the reaction the forward reaction. If the temperature on the equilibrium system is suddenly decreased, you are removing heat, which means you are favoring the forward reaction, so:
The value of Kc A. Increases: This is because the concentration of products is increasing and the concentration of reagents is decreasing.
The value of Qc C. Is less than Kc, because initially, the concentration of reagents was greater.
The reaction must A: Run in the forward direction to restablish the equilibrium.
The concentration of H2 will B. Decrease because the forward reaction is being favored, which means H2 is being consumed as a reagent.
Part 2:
This reaction is endothermic because the value of the enthalpy is positive, this means you need to add heat to the system to favor the forward reaction. If the temperature on the equilibrium system is suddenly increased you are favoring the forward reaction because you are adding heat, so:
The value of Kc A. Increases because the forward reaction is favored, so the concentration of products will increase and the concentration of reagents will decrease.
The value of Qc C. Is less than Kc because the initial concentration of reagents was greater that the current concentration.
The reaction must A. Run in the forward direction to restablish equilibrium.
The concentration of Br2 will A. Increase because it is a product in the forward reaction, so it is being produced.