Equilibrium Problems and LeChatelier's Principle Flashcards
For 2HI ⇌ H2 + I2, if [H2] changes by x, by what factor does [HI] change?
-2x
(stoichiometric coefficients)
Small x approximation only works if what condition is satisfied?
When [Change]/[Initial] is less than 5% for each species in the reaction
Does small x approximation work better when K is very large or very small?
When K is very small
Will adding more of a reactant change the equilibrium concentrations of a reaction?
Yes
Will adding more of a reactant change the K of a reaction?
No
Le Chatelier’s Principle: What happens when a system at equilibrium is disturbed?
It regains equilibrium through a reaction that counters the disturbance
2H2S (g) + O2 (g) ⇌ 2S (s) + 2H2O (g)
At equilibrium, if [H2S] and [O2], increase, in what direction does the reaction shift?
To the right. Corresponding increase in products to restore equilibrium
2H2S (g) + O2 (g) ⇌ 2S (s) + 2H2O (g)
At equilibrium, if [H2S] is removed, does [O2] increase or decrease?
Increases. The reaction shifts to the left to restore equilibrium, making more H2S and O2.
2H2S (g) + O2 (g) ⇌ 2S (s) + 2H2O (g)
At equilibrium, if [H2S] is removed, does [O2] increase or decrease?
Increases. The reaction shifts to the left to restore equilibrium, making more H2S and O2.
2H2S (g) + O2 (g) ⇌ 2S (s) + 2H2O (g)
At equilibrium, if [S] increases, what happens to [H2S]?
Nothing, stays the same.
Sulfur is a solid, doesn’t factor into Q or K. The system is still at equilibrium.
Le Chatelier’s Principle: If the pressure of a system at equilibrium increases and volume decreases, which way does the reaction shift?
Toward the side with fewer moles of gas or solution.
H2 (g) + I2 (g) ⇌ 2HI (g)
At equilibrium, pressure increases and volume decreases. Which way does the reaction shift?
No shift. Both sides have 2 moles.
2H2S (g) + O2 (g) ⇌ 2S (s) + 2H2O (g)
At equilibrium, pressure increases and volume decreases. Which way does the reaction shift?
Toward the right.
The right has 2 moles of gas
The left has 3 moles of gas
In a reaction, the changes in concentration that the species experience to achieve equilibrium are related by what?
The stoichiometric coefficients
A change in what condition causes a change in K?
Temperature
Does changing the concentration of a chemical species change K?
No
If volume increases, does the equilibrium shift to the side with more or less moles of gas?
More moles
Volume increases –> concentration decreases –> system form more moles to restore equilibrium
Does a change in pressure/volume change K?
No
At equilibrium, does increasing temperature shift the equilibrium toward endothermic or exothermic direction?
Endothermic direction to consume heat
At equilibrium, does decreasing temperature shift the equilibrium toward endothermic or exothermic direction?
Exothermic direction to produce heat
For an exothermic system, does an increase in temperature increase or decrease K?
Decrease K
For an endothermic system, does an increase in temperature increase or decrease K?
Increase K
