U1 s3 L3 Predicting the shift in equilibrium: Q vs K p 517 – 520 The effect of temp on K:p 526 Review Table p 528 Home work: p 519 # p 536 item: 17 p items: 9, 10 and 19 p 540 item: 30 Shifting the balance!

Upon completion of this lesson, you will be able to: determine whether a system is at equilibrium given concentration of system species and K. predict shifts in equilibrium positions using given concentration data (Q) for a system and K.

Le Châtelier's principle states that a system at equilibrium will respond to counteract the effect of a disturbance such as a change in concentration, pressure, and/or temperature. Disturbances that do not affect equilibrium are the addition of a catalyst, an increase in the surface area of a solid species, and a change in pressure when opposite sides of a system possess the same number of gas moles. Equilibrium constants (K values) are temperature dependent; that is, they only apply to systems at specified temperatures. A change in temperature changes the value of K (increase or decrease); however, no other disturbance has this affect on a K value.

Q vs: K Q is a reaction quotient based on the initial concentrations K is the equilibrium quotient based on equilibrium concentrations Three comparisons: Q = K the system is at equilibrium. (no shift) Q < K (shift forward to try to get products larger) In this case the initial size of the products is too small (compared to the reactants). The equilibrium will shift to try and increase the amount of product. Q > K (shift backward to try and get reactants larger) In this case the initial size of the products is too large (compared to the reactants). The equilibrium will shift to try and decrease the amount of product.

Q vs K : p 517 Based on the equation below K = 280 at 1000 K. In a 1.00 L flask mol of SO 2, 0.38 mol of O 2, and mol of SO 3 were combined 1000 K. Is the system at equilibrium? If not, then how will the concentrations of the three species have changed to establish the equilibrium ?

# 30 p 519 The following takes place inside a cylinder with a moveable piston. 2NO 2(g) ⇌ N 2 O 4 (g) At room temperature the equilibrium concentrations inside the cylinder are [NO 2 ] = mol/L and [N 2 O 4 ]= mol/L. a)Calculate the value of K b)Calculate the concentration of each species when the volume is halved (assume temp remains constant) c)Determine the value of Q. d)Predict the direction the reaction will proceed to re-establish equilibrium. Is this consistent with le chetalier’s principle?

The effect of Temp on the size of K - p 526

#33 p 529