Vocabulary
What type of K value would a reaction have if it's described as "going to completion"?
HUGE HUGE HUGE HUGE
What does Keq = 8.2 x 10-2 mean?
The reactants are favored.
In a homogeneous reaction, which chemicals count toward the equilibrium expression?
All of them
What direction will increasing concentration of oxygen shift the equilibrium?
4 NH3(g) +5 O2(g) <--> 4 NO(g) + 6 H2O(g) + heat
to the right
It is a biomacromolecule which serves as a catalyst for important biochemical reactions.
Interpret what it means for Q to be less than K.
1) The reaction is not currently at equilibrium.
2) The reaction will use more reactant and form more product by the time it reaches equilibrium.
Describe two practical limitations of using temperature to manipulate equilibrium.
Ex:
Cooling down slows both the forward and reverse reaction rates (one more so than the other), so it takes longer to get to equilibrium.
Heating up could cause some molecules to degrade.
2 SO2(g) + O2(g) <--> 2 SO3(g)
A catalyst is added to the above reaction. Discuss how the equilibrium is affected.
The reaction gets to equilibrium sooner, but the equilibrium itself doesn't change.
Define activation energy.
the additional energy necessary to go from reactants to the transition state's energy (or from products to TS if doing reverse reaction)
Write the equilibrium expression.
3 Ca2+(aq) + 2 PO43-(aq) <--> Ca3(PO4)2(s)
K = 1 / [Ca2+(aq)]3[PO43-(aq)]2
1) What do all catalysts do to assist a reaction?
2) What do the best catalysts also do in addition to #1?
1) lower Ea of the transition state by providing an alternative, energetically-easier reaction pathway
2) assist in directing chemicals together with proper orientation
For the following equilibrium, would you increase or decrease temperature to force the reaction in the forward direction?
H2(g) + CO2(g) <--> H2O(g) + CO(g)
delta H = 41.0 kJ
Increase
Describe what's the deal with the units of Q and K.
They differ according to the mathematical output of the equilibrium expression. They really don't mean much to us, so these units are usually ignored and not reported.
Write the chemical equation that Ksp represents for HCN(s).
HCN(s) <--> H+(aq) + CN-(aq)
You see a clear, colorless aqueous solution of unknown identity in the lab. You add some KCl to the flask and immediately see precipitation occur. You know that KCl is extremely soluble in water, so why is there suddenly a precipitate? Give the most reasonable answer.
There was something else dissolved in the water which was barely soluble. That something else was in equilibrium with K+ and/or Cl-. When you added KCl, the common-ion effect induced precipitation by increasing the concentration of one or both ions.
Draw a concentration graph that shows how the concentrations of the following chemicals change if a chemist removes carbon tetrachloride at equilibrium. Assume that products are favored.
CS2(g) + 3 Cl2(g) <---> S2Cl2(g) + CCl4(g)
Sudden drop in carbon tetrachloride and then some recovery
Gradual increase disulfur dichloride
Gradual decrease in both reactants (larger decrease for chlorine gas than carbon disulfide)
State the tenets of collision theory.
1) Molecules must collide to react.
2) Collisions must occur with sufficient energy for molecules to react.
3) Collisions must occur with appropriate orientation for molecules to react.
1) Draw a graph of concentration versus time that could correlate to a reaction where K = 6.8 x 1011.
2) Mark where you might be in the reaction if Q = 1.4 x 102.
1) should be lots more product than reactant at equilibrium
2) should be right after the cross-over from more reactant to more product
What is the most likely effect that adding more solvent will have on a reaction?
CHALLENGE QUESTION
What are all the ways a chemist could manipulate the system in order to shift the equilibrium of the following reaction to the left?
4 NH3(g) +5 O2(g) <--> 4 NO(g) + 6 H2O(g) + heat
Decrease volume while increasing pressure
Increase temperature
Add more product(s)
Remove reactant(s)