CHEMICAL REACTIONS

DEFINITIONS AND TYPES

REVISION:•DO NOT WRITE- FOR YOUR INFO ONLY

•We have looked at the period table, what atoms are,

elements and compounds

•You have learnt that atoms can join to make compounds

or molecules and that we can mix compounds to make

new compounds…..these are chemical reactions

•We also looked at metals and non metals etc

•Before we look in depth at Types of chemical reactions

we need to have some definitions straight…….Please

write the points on the next slide!

DEFINITIONS

Reaction- when something new is formed from an

interaction of substances

Reactants- The two or more substances used in the

reaction to form a new product

Product- the end result of the chemical reaction

Reaction rate- the speed of the reaction

SOME POINTS TO REMEMBER!AND WRITE!!!

Products have different properties than the substances

they were created from remember sodium chloride(table

salt- nasty explosive metal and smelly green gas- result

yummy nice white crystals for the hot chippies )

Reactions occur all around us- weathering of rocks,

rusting iron, and plants and animals decaying into the

soil

Some reactions are fast/some slow

te l l me some react ions you can think of that occur each day

Our body- digestion of food in the stomach- chemical

Cooking food- chemical e.g. eggs

Weathering as said- physical

Rusting- chemical

Respiration

Photosynthesis

Are there others you can think of??

REACTION RATES

Reaction Rates are affected by various factors• Temperature- hotter it is faster the molecules move and

faster reaction happens• Concentration- more you have of something in a certain

amount of solvent (i.e) water the more concentrated it is- the more there is to react with therefore the faster the reaction

• Dilute things have a small amount of solute compared to the liquid or solvent

• DRAW THE PICTURES ON NEXT SLIDE TOO , IN YOUR NOTES

DILUTE AND CONCENTRATED

CONCENTRATED DILUTE

REVISION –PARTICLE THEORY OF MATTER

1. Matter is comprised of tiny particles; i.e.: atoms and molecules.

2. Particles of matter are in constant motion.

3. Particles of matter are held together by strong electrical forces.

4. There are spaces between the particles that are very large

compared to the particles themselves

5 Temperature affects the speed of the particles. The higher the

temperature is, the faster the particles will move.

• the more concentrated a solut ion the better the

react ion as part ic les are c lose together

Reactions are also affected by how BIG the particles are- big pieces or finely

powdered- why??? Smaller the particles the greater the Surface Area….more

of the particle can react with something else and reaction is quicker- think

about burning a big log or small wood chips…..

Catalysts- A Catalyst is something which speeds up a chemical reaction but is

not actually part of the reaction- is not changed in any way

There are biological catalysts too!! These are called enzymes…we did that

early in the year in the human body unit…have a look back if you have

forgotten

http://www.kscience.co.uk/animations/ectopeptidase.swf

COULD DO MY SURFACE AREA PRAC/CATALYST IN MY FOLDER???

CHAPTER 3.1 PG 68Reactions can be affected by various things just discussed

All reactions also involve an energy change….energy is either

produced or needed for the reaction to happen- they are also

grouped into ENDOTHERMIC AND EXOTHERMIC type reactions

Endothermic- the energy is needed from the surroundings to

get the reaction to happen• Photosynthesis- WHO CAN EXPLAIN THIS TO ME??? PG 69 TEXT

• You need to know the equation again!!! Still!!!

• Sherbet making- we will see this in Acids and bases (yum )

EXOTHERMICEnergy is released in an exothermic reaction-

“exit” to go out…

Energy can be released in what ways?• Heat• Light• Sound• Electricity

We can see this when we have a reaction and we feel the test tube?? It may get hot, we burn things and see light and feel heat etc.

What exothermic reaction occurs in humans??? YES !! RESPIRATION

COMBUSTIONTHIS IS AN EXOTHERMIC REACTION- The reactants have

more energy than the product

Combustion occurs when things react with oxygen- BURNING• SOME combustion reactions are also called oxidation reactions• Bunsen burners, gas stoves produce HOT blue flames because

they burn methane or ethane gas in OXYGEN• WHEN OXYGEN IS SUPPLIED we can have complete combustion• IF WE RESTRICT THE oxygen- incomplete combustion• Incomplete Combustion doesn’t release as much heat/light etc.• These reactions are dirty!!! They release carbon /smoke/can

produce poisonous gases like carbon monoxide

POLLUTION/CLIMATE CHANGE

When we burn/combust things we release carbon dioxide

into the air

It is a greenhouse gas that traps heat in the atmosphere

The more we drive cars and be industrialized the more

carbon dioxide we produce

If we have incomplete combustion we also add the carbon

monoxide and create bigger problems for our earth

OTHER COMBUSTION REACTIONS

Mentioned earlier- Respiration is a combustion reaction in your

body

Combines sugar and oxygen that you breathe in – releases energy

for your cells to use

Waste product is again carbon dioxide!

Some combustion reactions do produce things that are not

carbon dioxide at all- magnesium when burnt in air – magnesium

oxide

Cracker combustion prac –page 76

CORROSION REACTIONS

Metals corrode when near water, air or other chemicals

Corrosion- means breaking down to make other compounds

E.g iron and steel react with water and oxygen in air to make rust!

Copper corrodes to form a green substance called Verdigris

Silver – tarnishes

Aluminium is very reactive- quickly forms a dull grey oxide-

doesn’t flake like rust…actually ends up protecting the rest of the

aluminium from corroding further…. Anodising

RUST

Iron and its alloy- steel are cheap

Most common metals used on earth

Both react with air and water to form Rust

Rust is Flaky, and dis-lodges and breaks down easily

We can protect from rust by painting or sealing the

metal in some way.

Unit review page 73- have a go at all questions

WRITING CHEMICAL EQUATIONS

Page 69 gives you the steps – lets work through

these together

You need to also learn the conservation of mass

formula/statement

NO ATOMS ARE LOST IN A REACTION JUST

REARRANGED

Conservation of mass prac – page 74