Chemical Reactions and Stoichiometry

Question 1

What are chemical formulae?

Answer 1

represent reactions and give quantitative information about the amounts of substances involved in reactions.

Question 2

What is stoichiometry?

Answer 2

the area of study that examines the quantities of substances consumed and produced in chemical reactions.

Question 3

What is The law of conservation of mass:

Answer 3

Atoms are neither created nor destroyed during any chemical reaction.

Question 4

How are chemical reactions represented in concise ways?

Answer 4

Chemical reactions are represented in a concise way by chemical equations.

Question 5

What do coefficients indicate in chemical equations?

Answer 5

Coefficients indicate the relative numbers of molecules of each kind involved in the reaction
We must have an equal number of atoms of each element on each side of the arrow.
When this condition is met, the equations is said to be balanced.

Question 6

Balance this equation:
H2O + O2 -> H2O

Answer 6

2 H2 + O2 = 2 H2O

Question 8

Balance CH4 + O2 = CO2 + H2O

Answer 8

CH4 + 2O2 CO2 + 2H2O

Question 9

What is a combination reaction?

Answer 9

When two or more substances react to form one product. This is typically where elements combine to form compounds.

EG: A + B –> C

or

CaO (s) + H2O (l) –> Ca(OH)2 (s)

Question 10

What is a decomposition reaction?

Answer 10

A single reactant breaks aprt to form two or more products. Many substances behave this way when heated. Eg:

C –> A + B

or

2NaN3 (s) –> 2Na (s) + 3N2 (g)

Question 11

What is a Combustion reaction?

Answer 11

Rapid reactions that produce a flame. Most of the combustion reactions we observe involve O2 from the air as a reactant. Eg: Combustion of propane:

C3H8 (g) + 5O2 (g) –> 3CO2 (g) + 4H2O (g)

Question 12

What are single Displacement/substitution reactions?

Answer 12

Single displacement or substitution where a more reactive element displaces a less reactive one.

eg:

2Na (s) + 2HCl (aq) –> 2NaCl (aq) + H2
(g)

Question 13

What are double displacement reactions?

Answer 13

Double displacement reactions, in which two compounds exchange ions to form different compounds

eg

NaCl (aq) + AgNO3 (aq) –> NaNO3 (aq) + AgCl (aq)

Question 14

What is a redox reaction?

Answer 14

Where there is a change in the oxidation number of the element, usually by the transfer of electrons to different elements or sites within a compound.

Fe (s) + CuSO4 (aq) –> FeSO4 (aq) + Cu (s)

Question 15

Chemical Formulae and chemical equations have a…

Answer 15

Chemical Formulae and chemical equations have a quantitative significance

Question 16

What do subscripts and coefficients represent?

Answer 16

precise quantities

Question 17

What is formula mass?

Answer 17

The formula mass of a substance is the sum of the atomic masses of each atom
in its chemical formula

Question 18

What is a mole?

Answer 18

A mole is the amount of matter that contains as many objects (atoms,
molecules, ions, UW students… etc) as the number of atoms in exactly 12 grams
of isotopically pure 12C

Question 19

What is avagadros number?

Answer 19

6.022 x 10 to the 23

Question 20

How does 1 mol and atomic mass of a single atom of an element relate to each other?

Answer 20

the mass of a single atom of an element (in amu) is numerically
equal to the mass (in grams) of 1 mol of that element.

Question 21

Details about molar mass?

Answer 21

A dozen is the same number (12) whether we have eggs or elephants, but clearly a dozen eggs does not have the same mass as a dozen elephants! However, the NUMBER is the same.

Similarly a mole is always the same number (6.022 x 1023), but 1 mole of different substances will have different masses

Question 22

What is the mass of 1 mole of 12C?

Answer 22

12g

Question 23

What is the mass of 1 mole of Cl?

Answer 23

35.5g

Question 24

What is the mass of 1 mole of Au?

Answer 24

197g

Question 25

What mass do we use when dealing with a refined isotope?

Answer 25

Mass of the isotope, otherwise, we use the average atomic mass of the element.

Question 26

What do coefficients of chemical equations show us?

Answer 26

Coefficients represent the numbers of molecules involved in a reaction and the mole concept allows us to convert this information to the masses of the substances.

Question 27

What do the coeffeicients in a balanced equation show us?

Answer 27

the relative numbers of molecules (or formula units) involved in the reaction and the relative number of moles

Question 28

What is a limiting reactant?

Answer 28

A reactant that is completely used up in a reaction is known as the limiting reactant because It limits the amount of product formed. The other reactants left over are sometimes called excess reactants.

Question 29

What is the actual yield?

Answer 29

The amount of product formed in the actual experiment.

Question 30

What is a theoretical yield?

Answer 30

The amount of product formed when all limiting reactant is used up in the reaction.

Question 31

Why is the actual yield almost always less than the theoretical yield?

Answer 31

The actual yield is almost always less than the theoretical yield due to:
* some reactants may not react.
* side reactions (undesired reactions) may occur.

Question 32

Is the actual yield ever greater than the theoretical yield?

Answer 32

The actual yield is never greater than the theoretical yield.

Question 33

What does the percent yield do?

Answer 33

The percent yield relates actual yield to the theoretical yield

Question 34

Formula for percent yield?

Answer 34

percent yield = (actual yield / theoretical yield) X 100%

Question 35

List the different alkanes and chemical formula which may be involved in combustion reactions.

Answer 35

1) CH4 = Methane
2) C2H6 = Ethane
3) C3H8 = Propane
4) C4H10 = Butane
5) C5H12 = Pentane
6) C6H14 = HExane