SCI: Moles and Molar Mass

Moles and Molar

Mass

Moles

◦Because the number of
particles involved in most
chemical reactions is so large,
chemists use a counting unit
called the mole (mol)

◦One mole (mol) is the amount
of a substance that contains
6.02 x 1023 particles of that
substance

2

Molar Mass

◦The mass in grams of one mole
of a substance is called its
molar mass

◦Just as the mass of a dozen
eggs is different from the
mass of a dozen watermelons,
different substances have
different molar masses

3

Multiple Choice

How many particles are in a mole?

• 602

• 602 million

• 602 moles

• 6.02 x 10²³

Multiple Choice

Molar mass is in units of ________.

• grams

• grams/mole

• mole

• moles/gram

Multiple Choice

Which would have more atoms?

• 1 mole of Li

• 1 mole of Au

• 1 mole of Si

• None, all are equal

Multiple Choice

Find the molar mass of $$H_2$$  

• 1.01g

• 2.02g

• 1.02g

• 2.01g

Multiple Choice

Find the molar mass of $$CaCO_3$$   

• 100.09g

• 100g

• 100.2g

• 101g

Multiple Choice

Find the molar mass of $$NH_3$$   

• 17.04g

• 17g

• 14.07g

• 17.03g

Calculating
Molar Mass
Example

Calculate the molar mass of CO2.

4

Calculating
Molar Mass
Example 2

Calculate the molar mass of
C6H10O5.

5

Mole-mass
conversions

◦Given the mass of a substance,
you can use the molar mass as
a conversion factor to
calculate the number of moles

6

Multiple Choice

Find the number of moles in 50.0g of NO2

• 2.50

• 1.08

• 50.0

• 3.08

Multiple Choice

Find the number of moles in 24 grams of NaHCO3 (round to nearest thousandths)

• .286

• .285

• .226

• .326

Mole-mass
conversions
Example 2

What is the mass of 0.2020 mol of
NO2?

8

Multiple Choice

What is the mass of 0.2020 mol of NO2?

• 10.454

• 4

• 9.292

• 8.10

Multiple Choice

what is the mass of 1.61 of H2O

• 28.98

• 82.12

• 22.981

• 3

Chemical

Reactions and

Energy

Energy
Exchanges

◦All chemical reactions release
or absorb energy!!!

◦This energy can take many
forms such as thermal energy,
light, sound, or electricity

10

More
Energy Out

◦Many reactions involve the
release of energy

◦Exergonic reactions: chemical
reactions that release energy

11

More
energy out
as thermal
energy

◦In many reactions, the energy
given off is thermal energy.

◦Exothermic reaction: when
the energy given off is primarily
in the form of thermal energy
◦Ex. wood burning and the
explosion of dynamite are
exothermic reactions

12

Multiple Choice

_____ reactions usually feel hot!

• endothermic

• exothermic

Multiple Choice

In an exothermic reaction, heat is ...

• taken in

• given out

Multiple Choice

If a chemical reaction is EXOTHERMIC, the temperature would....

• Stay the same

• Increase

• Decrease

More
energy in

◦Sometimes a chemical reaction
requires more energy to break
bonds than is released

◦Endergonic reactions:
chemical reactions that absorb
energy

13

Multiple Choice

If a chemical reaction absorbs light in a reaction, it is an

• exergonic reaction

• exothermic reaction

• endergonic reaction

• endothermic reaction

More
energy in
as thermal
energy

◦When the energy needed to
keep a reaction going is in the
form of thermal energy, the
reaction is called an
endothermic reaction

◦Ex. Baking bread, cooking an
egg, evaporating water

14

Multiple Choice

In an endothermic reaction, heat is ...

• taken in or absorbed

• given out or released 

Multiple Choice

A student mixed two chemicals to allow them to react. The temperature before the reaction was 25 ° C. The temperature after the reaction was 18° C. Which of the following is true?

• The temperature increased

• It is an endothermic reaction

• It is an exothermic reaction

Multiple Choice

During an endothermic reaction in a beaker if we are part of the surroundings and touched the beaker, it would feel _______. 

• Warm

• Cold

Multiple Choice

In an endothermic reaction, heat is ...

• taken in

• given out

Endothermic
vs.
Exothermic

15

Conservation
of energy in
chemical
reactions

◦Recall, energy can change from
one form to another, but the
total amount of energy never
changes

◦The total amount of energy
before and after the reaction
remains the same

16

Chemical energy of reactants = chemical energy of products + energy released

Multiple Choice

Baking bread and cooking an egg are examples of....?

• Endothermic processes

• Exothermic processess

• None of these 

Multiple Choice

What type of reaction is shown in the photo?

• Exothermic

• Isothermic

• Endothermic

• None of the  above

Multiple Choice

Is photosenthysis an Exothermic or an Endothermic reaction?

• Endothermic

• Exothermic

Multiple Choice

What type of reaction occurs in a hand warmer?

• exothermic

• endothermic

Multiple Choice

Have you ever eaten sherbet sweets candy? They fizz in your mouth and your tongue feels cold. Why do you think that is?

• It is an exothermic reaction

• It is an endothermic reaction

• It is made of ice

• It is dissolving your mouth