Equilibium constants and calculations

Equilibium constants and calculations

By Angela West

First a review!

Before we can begin working on doing the calculations, we need to make sure we're solid on writing formulas and balancing equations.

Chemistry is a balancing act! Yes, you have to deal with my bad puns.​

Multiple Choice

What is the correct formula for potassium oxide?

• KO

• K₂O

• KO₂

• K₂O₂

Multiple Choice

What is the correct formula for aluminum sulfate?

• AlS

• Al₂S₃

• Al₂SO₄₃

• Al₂(SO₄)₃

Draw

Write the formula for calcium nitrate

Draw

magnesium sulfate + aluminum phosphate --> magnesium phosphate + aluminum sulfate

Now on to equilibrium!

Because we all love math!

DON'T PANIC!

​Finding the equilibrium constant (K_eq) is easier than it looks

First let's look at the letter/symbols so we know what each one is and what it means.​

Nothing says confusing math like lots of weird symbols​

When you see brackets around a compound, it means the molar concentration (moles/liter)​

​Remember you must ALWAYS have a balanced equation

​What does [ ] around a letter mean?

​

These are representations of compounds​.

ex. NaCl, H₂O, NH₃​

​Upper case letters

​

These are representing the coefficients from the balanced chemical equation.​

​Lower case letters

​

Multiple Choice

The lower case letters in an equilibrium constant expression are

• Coefficients from the balanced equation

• Concentrations of the reactants and products

• Masses of the reactants and products

• The reactants and products

Multiple Choice

Brackets [ ] mean

• Moles

• Mass

• Molarity

• Multiply

Now let's review molar concentration

Remember concentration is how much solute you have dissolved in your solvent.

​

aka How many scoops of koolaid does Mrs. West put in a gallon of water?

answer: Entirely too many

Mrs. West likes her koolaid a bit too strong​ >.>

Draw

What is the molarity of 0.3moles of NaCl dissoved in 500mL of water?

Multiple Choice

If a reduced fraction has a value greater than 1, which one is larger?

• numerator

• denominator

• they're equal

Multiple Choice

If the K value (equilibrium constant) is 4.57x10⁹, which would be more favored?

• reactants

• products

• neither is favored

• both are equally favored

Multiple Choice

If your K value (equilibrium constant) is 1.0x10^-30, which will be favored?

• reactants

• products

• neither is favored

• both are equally favored

Now onto real calculations!

Try to contain your excitement!​

​Something to keep in mind

When doing equilibrium calculations, you MUST consider the phases of the reactants and products as mentioned previously.

​Anything that is a liquid or solid IS NOT COUNTED and doesn't impact the equilibrium calculation.

​

For example, the reaction:

NaOH(aq) + HCl(aq) <==> NaCl (aq) + H₂O(l)​ the K_eq = [NaCl]

[NaOH]​[HCl]

NOTE: the liquid water IS NOT INCLUDED​ in the K_eq

ICE charts will help you keep up with/organize your numbers

At the beginning of a reaction you have NO PRODUCTS

The H₂O given in the problem is something of an abnormality. You don't see product concentrations until the reaction has progressed.​

See? Easy stuff right?

One again, using an ICE box when working an equilibrium problem makes it WAY easier to keep up with all of your numbers/calculations.

​

Remember, when doing equilibrium calculations, anything that's a solid or a liquid in the reaction IS NOT COUNTED.

​

​

Draw

Now you try! For the equation:

SO₃(g) + H₂O(g) <==> H₂SO₄(g)

If [SO₃]=0.400M, [H₂O]=0.480M, [H₂SO₄]=0.600M what is the K_eq?

Draw

For the equation:

2SO₂(g) + O₂(g) <==> 2SO₃(g) at 25C the K_eq=798. If [SO₂]=4.20M and [SO₃]=11.0M, what is [O₂]?

Draw

For the equation: 2SO₃ <==> 2SO₂ + O₂

If 4.00moles of SO₂ and 5.00moles O₂ are present in a 2.00L container at equilibrium what is the equilibrium concentration and number of moles of SO₃ present if K_eq=1.47x10^-3

Draw

For the equation:

CO(g) + H₂O(g) <==> CO₂(g) + H₂(g)

If there are 1.60moles CO, 1.60 moles H₂O, 4.00 molesCO₂, and 4.00moles H₂ in an 8.00L container at equilibrium, what is the K_eq?

Draw

Calculate the K_eq for the equation: nitrogen monoxide (g) reacts with oxygen (g) to form nitrogen dioxide (g) if the concentrations are 0.160M, 0.122M, 0.129M respectively.

Draw

If we start with 0.100M CO₂ and H₂, what are the concentrations of products and reactants at equilibrium for the equation: CO₂ + H₂ <==> CO + H₂O