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What makes “superglue” bond instantly while PVA glue does not?

What makes “superglue” bond instantly while PVA glue does not? What factors determine how quickly food spoils? Why do “glow sticks” last longer when stored in the freezer?. Rates of reaction Rate = change in concentration (of reactant or product) time. Methods for measuring rate of reaction.

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What makes “superglue” bond instantly while PVA glue does not?

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  1. What makes “superglue” bond instantly while PVA glue does not? • What factors determine how quickly food spoils? • Why do “glow sticks” last longer when stored in the freezer?

  2. Rates of reactionRate = change in concentration (of reactant or product)time

  3. Methods for measuring rate of reaction 150g Collect a gas over time Follow a change in mass over time Formation of a precipitate or colour change over time.

  4. Factors affecting rate • Concentration (pressure with gases) • Temperature • Catalysts • Surface Area

  5. How doChemical ReactionsHappen?

  6. In Contact • Reactions don’t happen unless the substances are in contact.

  7. Why? • The particles of the reactants need to get together so that they can react.

  8. How does that work then? Reactant particles collide REACTION Product particles formed

  9. Is it really that simple? Yes Well, sort of. not really. OK, not quite!

  10. Not all collisions are effective • Paper burns • Paper + oxygen  carbon dioxide + water + nitrogen • The paper in this room isn’t burning. • It doesn’t have enough energy to burn. • If we make it hotter it will catch fire. • Paper burns on its own at 250 ºC

  11. A collision but with no effect Reactant particles collide Product particles not formed as there is not enough energy

  12. Reactions only happen if the particles have enough energy. The minimum amount of energy needed to start a reaction is called the Activation Energy The amount of activation energy needed is different for each reaction. But Every reaction has activation energy, they all need a little push to get started. Activation Energy

  13. More than the activation energy. Reactant particles collide REACTION Product particles formed

  14. O O O C O More than the activation energy. C Effective collisions, a reaction.

  15. The Collision Theory • Particles are constantly moving • For a chemical reaction to take place the reactant particles must collide first • For the collision to be successful the particles must have the right amount of energy • The minimum amount of energy required for an effective collision is called the activation energy

  16. Successful collisionsWhen two molecules collide a reaction might take place if:- The molecules have enough energy to overcome the activation energy- The molecules collide in the correct orientation

  17. Concentration • More particles in the same volume means they are closer together so greater chance of colliding. • More collisions means more collisions with energy greater than activation energy. • More frequent successful collisions means increased rate of reaction.

  18. Pressure • When the pressure is increased the same number of molecules occupy a smaller volume • For gaseous reactants this has the same effect as increasing the concentration. • More collisions take place, so more collisions with energy greater than activation energy. • More frequent successful collisions means increased rate of reaction.

  19. Catalysts A catalyst speeds up a reaction without being consumed by the overall reaction.

  20. Catalysts • Catalysts reduce the activation energy needed for a reaction • They do this by offering an alternate route for the reaction to take (for example via an intermediate) • Lower activation energy means more successful collisions • More successful collisions means faster rate

  21. Catalysts are very useful in industry • They often require lower temperatures than uncatalysed reactions, which reduces the energy demand and carbon dioxide emissions from fossil fuels. • They allow different reactions to be used with a better atom economy and reduced waste. • They are often enzymes which allow processes to operate at lower temperatures and pressures

  22. Examples of economically important catalystsIron in ammonia productionZiegler– Natta catalyst in poly(ethene) productionPlatinum/palladium/rhodium in catalytic converters

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