### 5.1 Exothermic and endothermic reactions

```5.1 Exothermic and
endothermic reactions
13 April 2015
What do the
words endo and
exo mean
before a word?
Exoskeletons
Endoskeletons
5.1 Exothermic and endothermic
reactions
13 April 2015
• Energy is involved in chemical reactions.
• Energy changes in a chemical reaction
can be measured.
The space shuttle main engines burn
hydrogen and oxygen in an exothermic
reaction at 3400°C. The three engines
produce the equivalent of 37 million
horsepower!
Exothermic reactions
• Exothermic reactions give out heat to the
surroundings e.g. burning, respiration
How can you tell a reaction is exothermic?
25o C
magnesium
Gets hot
Hydrochloric
acid
45o C
Heat
energy
given
out
Endothermic Reactions
Endothermic reactions cause a decrease in temperature.
Ammonium
nitrate
Cools
Water
Starts 25°C
Cools to 5°C
Heat
energy
taken
in as
the
mixture
returns
back to
room
temp.
Returns to 25°C
Measuring energy changes
Method
1.
2.
3.
4.
Measure 25 cm3 of copper sulfate solution
(HARMFUL) into the coffee cup.
Measure the temperature every 30 seconds for two
minutes.
Add 1 g of zinc powder (FLAMMABLE) to the cup
and quickly put on the lid and stir constantly.
Take the temperature every 20 seconds for three
more minutes.
Results
Draw a results
table to show the
temperature
changes over 5
minutes.
Questions
1. Plot your results as a graph. What do
during the reaction?
2. Is this reaction exothermic or
endothermic? How do you know?
3. How could you improve this
may be lost.
5.1 Exothermic and endothermic
reactions
13 April 2015
Most students should be able to:
• State a definition for exothermic and endothermic
reactions.
• List one example of an exothermic and endothermic
reaction.
• Recognise an endothermic or exothermic reaction
when data is given.
• Describe how a reaction can be monitored for its
energy changes.
Some students should also be able to:
• Explain the difference between exothermic and
endothermic reactions.
Quiz next
Exothermic or endothermic?
Hold up your card with ‘Exothermic’
or ‘Endothermic’ written on it to
vote!
Thermal decomposition of
marble?
Endothermic
Combustion of methane?
Exothermic
Photosynthesis?
Endothermic
Neutralisation of an acid and an
alkali?
Exothermic
Rusting of iron?
Exothermic
Thermal decomposition of copper
carbonate?
Endothermic
Respiration?
Exothermic
The End!
```