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CHEMICAL REACTIONS

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

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CHEMICAL REACTIONS

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  1. CHEMICAL REACTIONS DEFINITIONS AND TYPES

  2. 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!

  3. 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

  4. 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

  5. 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??

  6. 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

  7. DILUTE AND CONCENTRATED • CONCENTRATED DILUTE

  8. 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.

  9. 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 • http://www.kscience.co.uk/animations/ectopeptidase.swf • COULD DO MY SURFACE AREA PRAC/CATALYST IN MY FOLDER???

  10. 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 )

  11. 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

  12. 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

  13. 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

  14. 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

  15. 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

  16. 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

  17. 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

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