5.5 Rearranging Atoms

UNIT 5.5

Reactivity

LEARNING OBJECTIVES

By the end of unit 5.5 lesson you should be able to:

1.

Use word equations and symbol equations to describe reactions
(balancing symbol equations is not required)

2.

Understand that in chemical reactions mass and energy are conserved

Success Criteria

By the end of unit 5.5 lesson you should be able to:

I can use word and symbol equations to describe chemical reactions.
I can explain what is meant by the law of conservation of mass.
I can explain what is meant by the law of conservation of energy.
I can carry out practical work safely

Write the names and formulas
of all the acids you’ve learned.

Can you recall?

BELL RINGER

Write the 4 general equations
for making salts you’ve
learned.

Rearranging Atoms

In a chemical reaction, no atoms are lost. No new atoms are produced.

The atoms are simply rearranged into new combinations

Does any element that is present in the reactants disappears from the products? Do new element appear in the products?

Rearranging Atoms

Not only does it tell you which elements are present in the reactants and products but how many of each atom is present.

How many atoms of magnesium, hydrogen and chlorine can be found in the reactants?
How many atoms of magnesium, hydrogen and chlorine are in the products?

Open Ended

Look back at the reaction between copper carbonate and hydrochloric acid.

Which product of this reaction contains the element copper?

Open Ended

Look back at the reaction between copper carbonate and hydrochloric acid

Which reactant contains the element hydrogen?

Open Ended

Look back at the reaction between copper carbonate and hydrochloric acid

Which product contains the element hydrogen?

Fill in the Blanks

Fill in the Blanks

Rearranging Atoms

In the reaction between copper oxide and sulfuric acid:


copper oxide + sulphuric acid. ---> copper sulphate + water


a. Atoms of which elements are present at the start of the reaction?
b How many of each kind of atom are represented in the reactants shown in the equation?
c Atoms of which elements are present at the end of the reaction?
d How many of each kind of atom are represented in the products shown in the equation?

Match

copper oxide + sulphuric acid. ---> copper sulphate + water

How many of each kind of atom are represented in the reactants shown in the equation?

• Carbon

• Oxygen

• Hydrogen

• Sulfur

1 atom

5 atoms

2 atoms

1 atom

• 1 atom

• 5 atoms

• 2 atoms

• 1 atom

Match

How many of each kind of atom are represented in the products shown in the equation?

• copper

• oxygen

• hydrogen

• sulfur

1 atom

5 atoms

2 atoms

1 atom

• 1 atom

• 5 atoms

• 2 atoms

• 1 atom

Conservation of Mass

Atoms have mass.

If no atoms are gained or lost during a chemical reaction, then no mass is gained or lost either.

Challenge

Play and watch a video to explore and understand more about the conservation of mass. Take out your note and take down helpful information about conservation of mass.

Zara, Sofia and Marcus each make a prediction.

Discuss who you think is correct and give a reason for your answer.

Open Ended

Zara, Sofia and Arun carry out the reaction between calcium carbonate and hydrochloric acid. They place some calcium carbonate in a flask, add the hydrochloric acid and place the stopper in the top of the flask. They place the flask on a top pan balance. They each have different ideas about what will happen to the mass in the flask as the reaction takes place.

Discuss who you think is correct and give a reason for your answer.

Conservation of mass

Arun places a flask of hydrochloric acid on a top pan balance and carefully adds
calcium carbonate.
He measures the mass of the flask and the contents at the beginning of the reaction
and after 10 minutes. Question:

Write the word and symbol equation of this reaction.

Question:
In Arun’s experiment the mass appears to decrease. Why is this?

The carbon dioxide gas escapes into the
air because the flask is open.
You then cannot measure its mass

Calcium carbonate + hydrochloric acid → calcium chloride + water + carbon

dioxide

Let’s Read!
P199 - Another surprising result!

magnesium burning in oxygen

Energy and chemical reactions

​All chemical reactions involve energy.

Energy is used to break bonds in the reactants.

Energy is released when new bonds are formed in the products.

In this reaction, less energy is needed to break bonds in the reactants than is released when bonds form in the products. This is an exothermic reaction.

Look at the reaction between potassium and water

In the reaction between potassium and water the potassium catches
fire, gets so hot that it melts, burns with a pinkish purple flame and hisses or explodes. It also moves across the surface of the water.

In this reaction less energy is needed to break bonds in the reactants than is released when bonds form in the products. This is an exothermic reaction.

Is this an endothermic or exothermic reaction?

In other chemical reactions it takes more energy to break bonds in the reactants than is released when the bonds form in the products.

These reactions are called endothermic reactions and they take in energy.

Can you recall the law of conservation of energy?

sodium hydrogen carbonate + citric acid sodium citrate + water + carbon dioxide

Multiple Choice

What is an exothermic reaction?

• A reaction that absorbs energy

• A reaction that releases energy

• A reaction that does not involve energy transfer

• A reaction that occurs at a very low temperature

Multiple Choice

What is an endothermic reaction?

• A reaction that releases energy

• A reaction that absorbs energy

• A reaction that does not involve energy transfer

• A reaction that occurs at a very high temperature

Multiple Choice

In an endothermic reaction, the energy required to break bonds is:

• none of the choices

• Less than the energy released during bond formation

• Equal to the energy released during bond formation

• Greater than the energy released during bond formation

Multiple Choice

In an exothermic reaction, the energy released during bond formation is:

• Greater than the energy required to break bonds

• Less than the energy required to break bonds

• Equal to the energy required to break bonds

• none of the choices

Multiple Choice

Which of the following is an example of an exothermic reaction?

• Photosynthesis

• Evaporating water

• Combustion

• Melting ice

​Whether a chemical reaction takes in energy or releases energy there is no overall change in the amount of energy during the reaction.


This is because energy cannot be created or destroy. This is the law of conservation of energy.

Open Ended

State the law of conservation of energy.

SUCCESS CRITERIA

1.Use word and symbol equations to describe chemical

reactions.

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2. Explain what is meant by the law of conservation of mass.

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3. Explain what is meant by the law of conservation of

energy.

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4. Carry out practical work safely.

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