4.1 - Heat in Chemical Reactions

4.1 - Chemical Reactions

(pg.156-162)

1 - Identify conditions under which properties of a material are
changed, and critically evaluate if a new substance has been

produced

2 – Observe & describe patterns of chemical change by;

observing heat generated (exothermic) or absorbed

(endothermic) in chemical reactions

4 - Describe familiar chemical reactions, and represent these
reactions by using word equations and chemical formulas and

by constructing models of reactants and products

Review: Evidence of a

Chemical Change

How can you recognize a chemical change from a physical change?

Poll

PHYSICAL or CHEMICAL?

• Physical

• Chemical

Burning of wax to generate water and carbon dioxide is a chemical reaction.

Poll

PHYSICAL or CHEMICAL?

• Physical

• Chemical

Sublimation Melting

Condensation Evaporation

Deposition Freezing

​Physical State changes are PHYSICAL changes, not chemical changes!

Poll

PHYSICAL or CHEMICAL?

This is the Pharaoh’s Serpent (or Black Snake firework). The disgusting, growing mutant arm coil thing is actually mercury thiocyanate (Hg(SCN)2) getting lit on fire.

• Physical

• Chemical

Absolutely a Chemical Change!

​The mercury thiocyanate (Hg(SCN)2) getting lit on fire changes the chemical composition and thus creates a new product.

Review: Evidence of a

Chemical Change

• color change

• release or absorption of heat

(temperature change)

• formation of a solid (precipitate)

• formation of an odor

• gas produced

Review: Evidence of a

Chemical Change

• color change

• release or absorption of heat

(temperature change)

• formation of a solid (precipitate)

• formation of an odor

• gas produced

Chemical Reactions

compound A + compound B → compound C + compound D

Reactants

Products

Ex.
wood + oxygen 🡪carbon dioxide + water + energy released

Some CREATE heat

Some REQUIRE heat

​

Let's look into recognizing them!

​Chemical Reactions

Exothermic Reactions

Exothermic Reactions

(exo=out; thermic=heat)

● Think: exo = exit

A chemical reaction is exothermic if it:
➔ generates heat

➔ releases energy/heat into its surroundings

➔ causes an increase in temperature

You can feel heat or see light being produced.

Exothermic Reactions

Example: cellular respiration is exothermic

food + oxygen → carbon dioxide + water + energy

(C6H12O6 (s)+ O2→ CO2 + H2O + energy)

Can you think of any other examples of exothermic

reactions?

Multiple Choice

What is an exothermic reaction?

• Heat energy is released out to the surroundings

• Heat energy is absorbed by the substance.

• No energy is given out.

Multiple Choice

Exothermic reactions are occurring inside your body right NOW!

• True!

• False!

Multiple Choice

What type of reaction occurs in a hand warmer?

• Exothermic

• Endothermic

Multiple Select

Which of the following are examples of an exothermic reaction?

• rusting nail

• combustion

• burning magnesium

• Snow formation in clouds

Multiple Choice

What happens to the temperature in an exothermic reaction?

• It stays the same.

• The temperature decreases.

• The temperature increases.

Endothermic Reactions

Endothermic Reactions
(endo=in, thermic = heat)

A chemical reaction is endothermic if it:

➔ requires energy

➔ absorbs heat from the surroundings

➔ causes a decrease in temperature

Endothermic Reactions

Example: photosynthesis is an endothermic

reaction

energy + water + carbon dioxide → glucose + oxygen

(energy + 6H20 + 6CO2→ C6H12O6 + 6O2)

BAKING and COOKING EGGS are endothermic reactions!

Can you think of any other examples of

endothermic reactions?

Multiple Choice

Endothermic means energy is _____.

• absorbed

• released

Multiple Choice

______ reactions usually feel cold.

• Endothermic

• Exothermic

Multiple Choice

What happens to the temperature in an endothermic reaction?

• It stays the same.

• The temperature decreases.

• The temperature increases.

Physical Changes

ENDOTHERMIC

●

Some physical changes
absorb heat from the
surroundings.

●

For example, when water
evaporates, it absorbs heat
from its surroundings, so the
process of evaporation is
endothermic.

Heat + liquid water → water

vapour

EXOTHERMIC

●

Some physical changes
generate heat.

●

For example, when water
freezes, it releases heat to its
surroundings, so the process
of freezing is exothermic.

liquid water → ice+ heat

Multiple Choice

Which of the following physical changes are exothermic?

• Candle melting

• Dry ice (solid carbon dioxide) subliming to form gaseous carbon dioxide

• A puddle evaporating

• Water freezing to form ice.

Draw

Circle the EXOTHERMIC physical changes

What have you learned about Exothermic and Endothermic Chemical Reactions?

Heat - What do we know? Do we know things?

Let's Review!

Multiple Choice

Is this activity an endothermic or exothermic chemical reaction?

• Endothermic

• Exothermic

Multiple Choice

Is this exothermic or endothermic?

• Exothermic

• Endothermic

Multiple Choice

Is this exothermic or endothermic?

• Exothermic

• Endothermic

Multiple Choice

Is this exothermic or endothermic?

• Exothermic

• Endothermic

Writing Word Equations

When writing chemical word equations, the heat

released or required can be written as HEAT or ENERGY.

In an exothermic reaction, HEAT would be a _________.

In an endothermic reaction, HEAT would be a ________.

For example:

Gasoline + oxygen → carbon dioxide + water vapor + heat

Heat + baking soda + vinegar → sodium acetate + carbon dioxide + water

Multiple Choice

What is the correct word equation:

• copper (II) sulfate + iron sulfate --> iron + copper

• iron + copper (II) sulfate --> copper + iron sulfate

• iron + copper (II) sulfate = copper + iron sulfate

Multiple Choice

What is the correct word equation?

• sodium hydroxide + hydrochloric acid --> water + sodium chloride

• NaOH + HCl --> NaCl + H2O

• water + sodium hydroxide --> hydrochloric acid + sodium chloride

Now:

Complete Heat in Chemical Reactions handout

If you work efficiently, we can review the answers today and have time for a game!