Unit 3: stochiometry

Question 1

Theoretical yield?

Answer 1

Maximum amount of a given product that can be formed when the limiting reactant is completely consumed.

Question 2

Actual yield?

Answer 2

Actual amount produced in a reaction.

• Experimentally, reactions are never 100% efficient and product is lost along the way.
• Should always be smaller that theoretical yield, but can be greater in labs if measurements are not well done.

Question 3

Percent yield?

Answer 3

% yield = (Actual yield of product/theoretical yield of product) x 100

Question 4

Percent atom economy?

Answer 4

Ration of the molecular weight of the desired product to molecular weights (MW) of the reactants, expressed as percentage. Important for green chemistry. (Theoretical value)

% atom economy: (sum MW desired product/sum MW reactants - or total products) x 100

Question 5

What is a chemical reaction?

Answer 5

Process by which substances are converted to different substances

Question 6

Physical change?

Answer 6

Matter changes form but not chemical identity

Question 7

Law of conversion of mass?

Answer 7

• Matter is neither created nor destroyed, only transferred
• Numbers, and types of atoms, are identical on both sides of the reaction

Question 8

Steps for calculation masses of reactants and products in chemical reactions?

Answer 8

1. Balance the equation for the reaction
2. Convert the masses of reactants - or products - to moles
3. Use the balanced equation to set up the appropriate mole ratio
4. Use mole ration to calculated number of moles of the desired reactant - or product.
   5.Convert from moles to masses.

*Keep in mind, what do we want, what do we know and how to get there!

Question 9

Steps for stochiometry problems involving limiting reactants?

Answer 9

1. Always write balance equation for the reaction
2. Convert know masses of reactants to moles
3. Use appropriate mole ratios to determine which reactant is limiting
4. Compute the number of moles of the desired product
5. Convert from moles to grams with molar mass, if required

Question 10

Limiting reactant?

Answer 10

• Consumed firstly and completely
• Limits the reaction (limits the amount of product formed)

Question 11

Excess reactant?

Answer 11

• Any reactant not completely used up after the reaction, something remains!