Chapter 7 Test Flashcards
Le Chateliers principle
when a stress (such as changes in temperature, pressure or concentration) is applied to a system at
equilibrium, the reaction will respond in order to minimize the effect of that stress and return to equilibrium
What things can change the value of K, the equilibrium constant?
ONLY TEMPERATURE
How does a reaction shift when concentration of a reactant/product increases?
The reaction shifts away from that increased reactant/ product because that reactant/ product needs to be used up and things need to be rebalanced
How does a reaction shift when concentration of a reactant/product decreases?
Towards that reactant/product because now the reaction needs more of that reactant/product
How does a reaction shift if the pressure of a reaction increases?
It shifts toward the side with fewer moles of gas to alleviate some of the pressure being placed on the reaction
How does a reaction shift if the volume of the reaction increases?
If the volume increases, that means the pressure decreases. So the reaction shifts towards the side with more moles of gas to create more moles of gas.
How does adding an inert gas to a reaction at equilibrium affect it?
It will have no effect on the equilibrium because both sides of the reaction remain at equivalent partial pressures.
How does temperature change affect a reaction at equilibrium?
Heating or cooling a reaction will cause it to shift in the same manner as adding/removing a reactant or product. It depends on if the reaction endothermic or exothermic. If it is endothermic, then heat is a reactant basically. If it’s exothermic, heat is a product basically. Heating causes the reaction to shift away from heat in the reaction and cooling would shift the reaction towards heat in the reaction. Because if you add heat then you want to use up some and if you cool/lose heat, then you want to make more
How will catalysts affect a reaction at equilibrium?
It will not stress the system AT ALL. It will decrease reaction rates and help a reaction reach equilibrium faster.
Study 7.1-7.8 Quizlets
How do you come up with the answer to “How will the value of K change if the reaction is heated?”
When you heat a reaction think of which way it will shift, and if products or reactants increase think of how that affects K and that is how you get your answer
If Q is less than K which reaction is favored?
The forward/ products
If Q is more than K which reaction is favored?
Reverse/ reactants
How do you move forward if you are given starting concentrations for all reactants and products and the K value?
Determine the Q value by using the initial values then compare it to K. Depending on if it is larger or smaller than K, it will let us know if we proceed to reactants or products. Whichever way we proceed, we add x or whatever in the change part of our ICE table. Then, solve using ICEd tables.
How are volume and pressure related?
They are inversely related so if volume is halved, pressure is doubled.
Ksp
The maximum amount of ions that can be present in the solution before a precipitate appears
Something important to remember about Ksp
THEY NEVER HAVE DENOMINATORS
bc solids will always be the reactants and they are not ever included in a K expression
What does a high Ksp value mean?
That the solid will dissolve more
What does a low Ksp value mean?
That less of the solid will dissolve
When is the only time you can compare Ksp values for solubility?
When they form compounds in the same ratio
How do you answer the question “Will a precipitate form if…”?
First, write the equation for the thing you are given Ksp for. Then, write the Ksp expression. Then, work on the Qsp equation to find the Q value. If you are given concentration values you need to divide the original volume by the new one(volume is additive), then multiply by the old concentration. Then, plug those new concentrations in and if Q is bigger than K a precipitate will form. If Q is smaller than K a precipitate will not form.
Why would a precipitate form if Q is bigger than Ksp?
Because the solution is supersaturated and can’t keep all the Mg²⁺ and OH⁻ ions dissolved. As a result, Mg(OH)₂ will form a precipitate.
Why wouldn’t a precipitate form if Q is smaller than Ksp?
The solution is unsaturated. This means there’s still room to dissolve more Mg(OH)₂, so no precipitate forms.
How do you calculate molar solubility?
Molar mass times solubility of the compound
How do you know what will precipitate first in a reaction?
Whatever requires the least concentration of the compound to reach equilibrium
What is the common ion effect?
If you a solid is added to a solution that contains one of the same ions as the solid, less of the solid will dissolve than it would into a “random” solution
How does the common ion effect affect precipitates?
If you add a solid to a solution that contains one of the same ions as the solid, then the reaction will shift to the reactants and more precipitate will form.
Should you worry about solids in an ICE table?
NO
Where is the common ion typically always added?
Into a solution using one of the SNAP ions
Sodium
Nitrate
Ammonium
Potassium
How do you answer “Calculate the molar solubility of solid when it is dissolved in a common ion solution. The Ksp is..)
Make the Ksp expression. Then make an ice table. Whatever the common ion is, the molarity of the solution is the molarity of the ion. Then fill out the ice table and solve for x which will be the molar solubility.
