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Tutorial Index

Introduction to Elements, Atoms, Molecules,
Compounds and Chemical Bonding

Introduction to Chemical Bonding
Metals, Non-metals and Compounds
Non-metal Radical Groups
Names of Acids and other compounds
Types of Chemical Reactions I
Types of Chemical Reactions II
Introduction to the Periodic Table
Using Chemical Formulae
Balancing Chemical Equations

The Chapters Index

 

Chemical Reactions : The Rules

Reaction 3

 

Reaction 4

"Matter can neither be created nor destroyed by chemical means"

This is a really important rule to remember when you are making chemical equations. You must always make sure that you have the same number of each type of atom on either side of the chemical equation. You cannot lose or gain any atoms!

Take another look at the two equations above.

In the first equation you will find one carbon atom and two oxygen atoms on either side of the reaction arrow

In the second equation there are two nitrogen atoms and six hydrogen atoms on the reactants' side of the equation. There are the same numbers on the products' side.

Atoms have neither been created or destroyed, they have simply been rearranged to make different molecules.

 

 

THE LANGUAGE OF CHEMISTRY

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Chemical Reactions

Atoms are re-arranged during a chemical reaction, they are not changed by the reaction.

A chemical reaction is shown like this:

Chemical reaction

The reaction shown below represents the element carbon burning in air. It combines with the oxygen gas in the air to make carbon dioxide gas.

Reaction 3

One atom of carbon (4 bonding arms) reacts with one molecule of oxygen gas)

The carbon and oxygen gas need to be heated together for this reaction to proceed.

During the reaction the two oxygen atoms were separated and then joined to the carbon atom.

 

In the next example nitrogen gas reacted with hydrogen gas to form ammonia gas.

Reaction 4

One molecule of nitrogen gas reacts with three molecules of hydrogen gas.

These gases need to be heated together for the reaction to proceed.

The reaction produces two molecules of ammonia gas.

 

Chemical Reactions : The Products of a Reaction

Chemists find the identity of the products of a reaction by experimentation and observation. Study the reaction below:

Reaction 5

 

In this reaction hydrogen sulfide gas is burnt in oxygen gas. The products of this reaction are sulfur and water.

If hydrogen sulfide gas and oxygen gas are mixed in a gas jar and a burning match or taper is placed near the mouth of the gas jar. A bright, blue flame can be seen that moves down the gas jar. When the reaction is finished you can see a yellow powder on the inside of the gas jar as well as condensation.

This yellow powder is the element sulfur. The arrow in the equation tells you that a solid has been made during the reaction. The condensation can be proved to be water by testing with cobalt II chloride paper which turns from blue to pink only in the presence of water.

 

Chemical Reactions : The Products of a Reaction

The equation below shows what happens when chalk (calcium carbonate) is heated.

Reaction 6

 

This reaction is an example of chemical decomposition by heat. The two products are calcium oxide and carbon dioxide gas.

The gas can be proved to be carbon dioxide by bubbling it through lime water. Lime water is a specific test for carbon dioxide gas. No other gas will make the lime water turn "cloudy" or "milky".

 

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