Chapter 4- Chemical Equilibrium Flashcards
How do we determine whether the reactants or products are favoured on a graph of the two?
(Page 184)
Products start at zero and which ever equilibrium line is higher on the graph is favoured
What exactly is equal at equilibrium?
The rates of the reactions
NOT the concentrations
What is the equation for the equilibrium constant (K) for the reaction:
aA + bB cC + dD
K= ([C]^c [D]^d)/([A]^a [B]^b)
[ ] means molar concentration of element
What is the law of mass action?
The relationship between the balances chemical equation and the expression of the equilibrium constant
Which direction of the reaction is favoured when the equilibrium constant (K) is much larger than 1?
Roughly equal to 1?
Much less than 1?
Larger- forward reaction is favoured
Roughly equal- neither reaction is favoured, forward proceeds about halfway
Smaller- reverse reaction favoured
What happens the the equilibrium constant (K) equation when you:
a) reverse the equation?
b) multiply the coefficients in the equation by n?
c) add two or more chemical equations to obtain an overall equation?
a) invert the K equation
b) put the K equation to the power of n, (…)^n
c) multiply the corresponding equilibrium constants by eachother to obtain overall constant
Ex: K1= A 2B
K2= 2B 3C
Koverall= K1 (K2)
What are the two ways we can express the equilibrium constant in terms of?
Concentration- Kc (moles/litre)
Partial pressures of gases- Kp (atm)
They are not unitless since those units cancel
How do you find the concentration of an ideal gas A given the number of moms and the volume in litres?
[A]= n/V
PV=nRT
P=n/V (RT)
P=[A]RT
What is the equation that connects Kc to Kp?
Kp= Kc(RT)^(c+d-(a+b))
What states of matter are not included in the equilibrium expression?
Solids, liquids
If given the concentration of one compound in an equilibrium, how do you find the other concentrations?
Use stoichometry
If no initial concentration is given for an element in an ICE question, what do we assume it’s concentration is?
0 M
What is the reaction quotient (Qc)?
The ratio at any point in the reaction of the concentrations of the products raised to their stoichiometric coefficients divides by the concentrations of the reactants raised to their stoichiometric coefficients
Qc= ([C]^c [D]^d) / ([A]^a [B]^b)
This is used to determine how close a reaction is to equilibrium
What is the reaction quotient with a reaction mixture containing only reactants?
Only products?
Perfect equilibrium?
Only reactants- 0
Only products- infinity
Equilibrium- it will equal the exact value of K
QK- goes to left
How do you find equilibrium concentrations when giving the equilibrium constant and all but one of the equilibrium concentrations?
Use the Equation for K of products over reactants and re arrange to solve for concentration of missing element
Do example questions on finding equilibrium concentrations from initial concentrations and the equilibrium constant.
Page 215-217
Aight
What does it mean to approximate an equilibrium problem?
How do we check the validity?
Mean to cross out any x that will result in a small change when added or subtracted to a bigger value
Ex: 1-x would be small because we know x is small so it would barely affect 1
We check this by taking the ration of x divided by the number it was subtracted from and timesing it by 100, if it’s less than 5% you good
What is Le Chatelier’s Principle?
States that when a chemical system or equilibrium is disturbed, the system shifts in a direction that minimizes the disturbance
What happens if we increase the concentration (add more) of the reactants of an equilibrium reaction?
The reaction will shift right
What states of elements will not be affected when increasing concentration, volume, or pressure?
Solids
Liquids
What happens to an equilibrium reaction when the volume of reactants is increased?
Increase in volume=decrease in pressure
The reaction will shift to the side with more moles of gas
What happens to an equilibrium reaction when the volume of reactants is decreased?
Decrease in volume= increase in pressure
The reaction will shift to the side with less moles of gas
How do catalysts or inert gases at constant volume change the equilibrium?
They do not change the equilibrium
How does the temperature change affect the equilibrium shifting?
Temperature=heat
Exo- heat in products
Endo- heat in reactants
The reaction will shift to the side opposite of where heat was added
