Stoichiometry

What is Stoichiometry• Using a balanced chemical equation to

determine how much reactant or product is consumed or produced in a chemical reaction.

• 2 H2 (g) + O2 (g) 2 H2O (l)– How many moles of H2O are produced from the

reaction of 2 moles of H2?

– How many moles of O2 are required to produce 4 moles of H2O?

Chemical Equations

• 2 H2 (g) + O2 (g) H2O (l)

http://www.chemistry.ohio-state.edu/betha/nealChemBal/

4 moles molecules + 2 moles molecules 4 moles molecules

Coefficients in Chemical Equation represents mole ratios

Stoichiometry“Chemical Equation = recipe”

• 2 bread slices + 1 cheese slice 1 sandwich

– Suppose need to make as many cheese sandwiches as possible for a party and have 20 slices of bread...how many slices of cheese are needed?

• By inspection of recipe (chemical equation)• Or use coefficient ratio (mole ratio) from equation: – 2 bread slices = 1 cheese slice

• cheese slices = 20 bread slices x

= 10 cheese slices needed

slices_bread2

slice_cheese1

Image source: http://www.fotosearch.com/clip-art/sandwich.html

Mole – mole problem

Molar Mass Review

Mole-Mass problems

Mass-Mass Problems

Try the following:How many moles of Fe2O3 will be produced from the reaction of 1.50 mol of iron with Oxygen?

a) Write the balanced equation– 4 Fe + 3 O2 2 Fe2O3

b) Solve– ….mol Fe2O3 = 1.50 mol Fe x

= 0.75 mol Fe2O3 molFe4

OmolFe2 32

Using grams:Consider the unbalanced reaction:

Al (s) + Fe2O3 (s) Al2O3 (s) + Fe (l)

If you react 4.0 g of Al with excess Fe2O3, how many moles of Fe will be produced??

• First balance the equation:2 Al (s) + Fe2O3 (s) Al2O3 (s) + 2 Fe (l)

• Chemical equation speaks to us in moles, not grams! So to use the mole ratio it gives us (2mol Al: 2 mol Fe), – first need to convert 4.0 g Al to moles of Al– Then take moles of Al and “convert” to moles of Fe using mole ratio from

balanced equation (coefficient ratio) as was done on previous slides.

Molar Mass of Al is 26.98 g

Molar Mass of Fe is 55.85 g

4.0 g Al 1 mole Al 2 mole Fe 55.85 g Fe= 8.3 g Fe

26.8 g Al 2 mole Al 1 mole Fe