Photosynthesis uses solar energy to convert carbon dioxide into glucose, which is stored as carbohydrates.

carbon dioxide + water + sunlight energy glucose + oxygen 6CO2 + 6H2O C6H12O6 + 6O2

All living things release energy from carbohydrates during respiration.

glucose + oxygen carbon dioxide + water + energy C6H12O6 + 6O2 6CO2 + 6H2O

Lightning causes nitrogen in the air to form nitrates.

nitrogen + oxygen nitrogen dioxide N2 (g) + 2O2 (g) 2NO2 (g)

Carbon dioxide dissolves in water to form carbonic acid.

carbon dioxide + water carbonic acid CO2 (g) + H2O (l) H2CO3 (aq)

?What natural chemical

reactions are suggested in these pictures?

Reactions in nature are all around us. Could we stop or reverse them if we tried?

42Chemical Reactions Student Guide Part 3 Energy and change

Activity type

Activity 3.4 Reactions in nature

Concept map

All living things need energy to function and grow and this happens through chemical reactions. These reactions also shape the environment around us and produce new chemicals.

What to do:

In a group, create a Concept Map to illustrate reactions in nature. Don’t forget to include reactions in living things, as well as reactions in the atmosphere and lithosphere. Use a key to highlight reactions which are:• beneficial and not-so

beneficial• short and longer term.

CONCEPT MAP

CHEMICAL REACTIONS

MANY TYPES

DIFFERENT RATES OR SPEEDS

DEPENDING ON

NEW SUBSTANCES FORM, OLD ONES

DISAPPEAR

SIZE/SURFACE OF PARTICLES

CONCENTRATION

SYNTHESIS

REACTIONS INVOLVING LIGHT

COMBUSTION REACTIONSNEUTRALISATION

REACTIONS

DECOMPOSITION

PRECIPITATION REACTIONS

PRESENCE OF CATALYST

TEMPERATUREha

ppen

at

ther

e ar

e

BUBBLES FORM

REACTION BETWEEN A FUEL AND OXYGEN TO RELEASE ENERGY

e.g. hydrogen (g) + oxygen (g) water (l)

REACTION BETWEEN AN ACID AND A

BASESOLID PRODUCTS

e.g. making cheese

COLOUR CHANGES

TEMPERATURE CHANGE

Chemical Reactions Student Guide Part 3 Energy and change 43

Activity 3.4 Reactions in nature Continued

Fermentation rates

Organisms such as yeast can release energy without using oxygen by the process of "fermentation".

glucose carbon dioxide + alcohol + energy C6H12O6 (aq) 2CO2 (g) + 2C2H5OH (g)

In this investigation you will design an experiment to find out more about fermentation.

What to use:

Each PAIR will require:

• 4 or 5 small soft drink bottles• sachets of dry yeast (1 g per bottle)• teaspoon• 4 or 5 round balloons • 250 mL each of a variety of fruit

juices.

Each STUDENT will require:

• safety glasses• Science by Doing Notebook.

What to do:

Your task is to design and carry out a fair test to compare the rates of fermentation in different fruit juices.

Step 1Decide on an hypothesis and aim for your experiment.

Step 2Plan your experiment, making sure it:• answers the aim

• is carried out in controlled conditions

• is reliable (don’t forget replication).

Step 3Carry out your experiment, Notebooking your results as you go.

Step 4Write a full report on your experiment under the correct headings.

Discussion:

In your discussion, make sure that you:• include a graph and inferences

from the data you have collected• explain any differences in

fermentation rate• discuss whether your hypothesis

was correct• suggest improvements to your

experimental design.Can you suggest a more reliable way of confirming your findings?

WRITE A...

GOGGLESGLOVES

LAB COATSHOES

Click here to learn more about energy changes in the environment.

Chemical Reactions Student Guide Part 3 Energy and change 44

Activity 3.4 Reactions in nature Continued