CHEM 162 LAB #6 SYNTHESIS OF ASPIRIN
COMPLETE SOLUTION EXAMINATION TEST
2026 FULL QUESTIONS AND SOLUTIONS
GRADED A+
⩥ Determining equilibrium constant. Answer: Most direct way of
finding K is to measure the amounts of reactants + products in a mixture
AT EQUILIBRIUM!
(So, K depends on the reaction)
*** REMEMBER: ONLY GAS + AQUEOUS
REACTANTS/PRODUCTS GO IN THE EQUILIBRIUM
EXPRESSION!!!
The equilibrium mixture may have different AMOUNTS of reactants +
products based on how much material was there to begin, but the value
of K will ALWAYS BE THE SAME, AS LONG AS TEMPERATURE
IS KEPT CONSTANT!!!
(REMEMBER: value of K is INDEPENDENT of initial amounts of
reactants + products)
⩥ How do you solve for the missing variable when you don't know
equilibrium concentrations and/or K to plug directly into the equilibrium
expression?. Answer: You have to use the equilibrium expression,
,stoichiometric coefficients, and initial concentrations when given to find
the missing information!
- ICE Box method for the equation!!!
Initial (M)
Change (M)
Equilibrium (M)
* Always write the generic expression (what you know) first!
* Remember: K is unitless!!!
- Quadratic formula from ax^2 + bx + c = 0
You don't always have to use the quadratic formula - if the amount of
species used to reach equilibrium is VERY SMALL compared to the
initial amount of the species, than we can disregard x compared to the
initial amount! This may prevent us from having to use the quadratic
formula!
⩥ What if K is very small or very large?. Answer: If K is LARGE, the
reaction lies to the right (a lot of reactants will be used to make
products), so there will be a large change from the initial concentration
of reactants to equilibrium concentration of reactants) - assuming x is
very small compared to the initial amount + disregarding it in the
denominator will probably NOT BE VALID!
,If K is SMALL, the reaction lies to the left (less reactants than products),
so the change from initial concentration to equilibrium concentration
will be very small (assuming x is very small compared to the initial
amounts + disregarding it in the denominator will probably be VALID)!
*** RULE OF THUMB: If K <= 10^-5, assume the reaction lies to the
LEFT (towards reactants) + that K IS SMALL! DISREGARD X IN
THE DENOMINATOR! Then, make sure to check if the assumption is
valid by the 5% RULE!
⩥ Equilibrium Approximation: 5% Rule. Answer: By convention, we
accept that the assumption is valid if x is less than 5% of the initial
concentration
Once you solve for x without using the quadratic formula, check that x <
5% of initial concentration:
- If it IS less than 5% of initial concentration, you're done!
- If it is MORE than 5% of initial concentration, you need to resolve for
x using the quadratic equation (not disregarding x)!
⩥ Reaction Quotient (Q). Answer: = numerical ratio of PRODUCTS :
REACTANTS (just like K) at SOME POINT in a reaction's progress, not
necessarily at equilibrium!
, Gives us a way of determining if a reaction has reached equilibrium or
not! Depending on the value of Q, we can determine which way the
reaction must go in order to reach equilibrium.
Q < K : reaction is NOT at equilibrium, the reaction needs to proceed in
the FORWARD direction to produce MORE PRODUCTS in order to
reach equilibrium
Q > K : reaction is NOT at equilibrium, reaction needs to proceed in the
REVERSE direction to produce LESS PRODUCTS in order to reach
equilibrium
Q = K : reaction is AT EQUILIBRIUM
⩥ Le Chatelier's Principle. Answer: If a system is at equilibrium and a
change is made to the system, then the reaction will counteract the
change to reestablish equilibrium
4 ways to affect equilibrium:
1) Changing CONCENTRATION of reactants/products
2) Changing TEMPERATURE of reaction
3) Changing VOLUME/PRESSURE of reaction
4) Adding a CATALYST/NOBLE GAS to reaction
COMPLETE SOLUTION EXAMINATION TEST
2026 FULL QUESTIONS AND SOLUTIONS
GRADED A+
⩥ Determining equilibrium constant. Answer: Most direct way of
finding K is to measure the amounts of reactants + products in a mixture
AT EQUILIBRIUM!
(So, K depends on the reaction)
*** REMEMBER: ONLY GAS + AQUEOUS
REACTANTS/PRODUCTS GO IN THE EQUILIBRIUM
EXPRESSION!!!
The equilibrium mixture may have different AMOUNTS of reactants +
products based on how much material was there to begin, but the value
of K will ALWAYS BE THE SAME, AS LONG AS TEMPERATURE
IS KEPT CONSTANT!!!
(REMEMBER: value of K is INDEPENDENT of initial amounts of
reactants + products)
⩥ How do you solve for the missing variable when you don't know
equilibrium concentrations and/or K to plug directly into the equilibrium
expression?. Answer: You have to use the equilibrium expression,
,stoichiometric coefficients, and initial concentrations when given to find
the missing information!
- ICE Box method for the equation!!!
Initial (M)
Change (M)
Equilibrium (M)
* Always write the generic expression (what you know) first!
* Remember: K is unitless!!!
- Quadratic formula from ax^2 + bx + c = 0
You don't always have to use the quadratic formula - if the amount of
species used to reach equilibrium is VERY SMALL compared to the
initial amount of the species, than we can disregard x compared to the
initial amount! This may prevent us from having to use the quadratic
formula!
⩥ What if K is very small or very large?. Answer: If K is LARGE, the
reaction lies to the right (a lot of reactants will be used to make
products), so there will be a large change from the initial concentration
of reactants to equilibrium concentration of reactants) - assuming x is
very small compared to the initial amount + disregarding it in the
denominator will probably NOT BE VALID!
,If K is SMALL, the reaction lies to the left (less reactants than products),
so the change from initial concentration to equilibrium concentration
will be very small (assuming x is very small compared to the initial
amounts + disregarding it in the denominator will probably be VALID)!
*** RULE OF THUMB: If K <= 10^-5, assume the reaction lies to the
LEFT (towards reactants) + that K IS SMALL! DISREGARD X IN
THE DENOMINATOR! Then, make sure to check if the assumption is
valid by the 5% RULE!
⩥ Equilibrium Approximation: 5% Rule. Answer: By convention, we
accept that the assumption is valid if x is less than 5% of the initial
concentration
Once you solve for x without using the quadratic formula, check that x <
5% of initial concentration:
- If it IS less than 5% of initial concentration, you're done!
- If it is MORE than 5% of initial concentration, you need to resolve for
x using the quadratic equation (not disregarding x)!
⩥ Reaction Quotient (Q). Answer: = numerical ratio of PRODUCTS :
REACTANTS (just like K) at SOME POINT in a reaction's progress, not
necessarily at equilibrium!
, Gives us a way of determining if a reaction has reached equilibrium or
not! Depending on the value of Q, we can determine which way the
reaction must go in order to reach equilibrium.
Q < K : reaction is NOT at equilibrium, the reaction needs to proceed in
the FORWARD direction to produce MORE PRODUCTS in order to
reach equilibrium
Q > K : reaction is NOT at equilibrium, reaction needs to proceed in the
REVERSE direction to produce LESS PRODUCTS in order to reach
equilibrium
Q = K : reaction is AT EQUILIBRIUM
⩥ Le Chatelier's Principle. Answer: If a system is at equilibrium and a
change is made to the system, then the reaction will counteract the
change to reestablish equilibrium
4 ways to affect equilibrium:
1) Changing CONCENTRATION of reactants/products
2) Changing TEMPERATURE of reaction
3) Changing VOLUME/PRESSURE of reaction
4) Adding a CATALYST/NOBLE GAS to reaction
