Stoichiometry

Question 1

Are coefficients in chemical equations always representations of individual molecules?

Answer 1

No. They can represent molecules and moles.

Question 2

Which of these must always be conserved in a chemical reaction: Mass, number of atoms, and number of molecules?

Answer 2

Mass and number of atoms must always be conserved. Number of molecules is not always conserved.

Question 3

What are mole ratios?

Answer 3

Conversion factors based on the coefficient numbers of two products/reactants in a chemical equation. It relates the amounts of any two substances in the reaction.

Question 4

What is stoichiometry?

Answer 4

Determining the qualitative relationships between reactants and products in a chemical reaction

Question 5

Can you multiply each coefficient by the same term and still have an accurate chemical equation?

Answer 5

Yes. Ex: 3 H2 + 1 N2—> 2 NH3 can also become 30 H2 + 10 N2—> 20 NH3.

Question 6

3 H2 + 1 N2—> 2 NH3 What is the ratio of H2 to NH3?

Answer 6

3 H2/2 NH3

Question 7

What can you do with stoichiometry?

Answer 7

You can use a balanced chemical equation to identify quantities of reactants and products.

Question 8

How do you convert from moles of a given substance to the moles of the substance in question?

Answer 8

(moles given)(moles question/moles given)= moles question

Question 9

How do you convert from mass of a given substance to the moles of the substance in question?

Answer 9

(grams given)(1 mole given/grams given)(moles question/moles given)= moles question

Question 10

How do you convert from moles of a given substance to the mass of the substance in question?

Answer 10

(moles given)(moles question/moles given)(grams question/1 mole question)= mass question

Question 11

How do you convert from mass of a given substance to the mass of the substance in question?

Answer 11

(grams given)(1 mole given/grams given)(moles question/moles given)(grams question/1 mole question)

Question 12

What is the actual yield?

Answer 12

The actual (or experimental) yield is the amount of product actually recovered from an experiment. It is a data-derived value.

Question 13

What is the theoretical yield?

Answer 13

The possible yield, the maximum amount of product that could be produced from the reactants. It is a value derived from a stoichiometry calculation.

Question 14

What is percent yield?

Answer 14

The actual yield compared to the theoretical yield; this determines experimental accuracy.

Question 15

How do you calculate percent yield?

Answer 15

(Actual yield/theoretical yield) x 100

Question 16

What does a scientist aim for with percent yield when doing an experiment?

Answer 16

100%

Question 17

What is a limiting reactant?

Answer 17

The reactant that runs out first in a chemical reaction; it determines theoretical yield.

Question 18

What is an excess reactant?

Answer 18

The reactant of which there is plenty in order to finish the reaction.