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

tell me some reactions 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 solution the better the reaction as particles are close 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   COULD DO MY SURFACE AREA PRAC/CATALYST IN MY FOLDER?? ?

CHAPTER 3.1 PG 68  Reactions 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 )

EXOTHERMIC  Energy 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

COMBUSTION  THIS 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