Chemistry—> Rates of reactions

• What other factors can change the active site of enzymes and denature them?

  PH
• What can happen to enzyme if they're used at temperatures above 40°C

  Enzymes become denatured. This is because at higher temperatures, some intermolecular forces between protein chains break so the enzyme changes its shape thus the active site of the enzyme has changed its shape, and the substrate no longer fits into the actuve site.
• How do enzymes work?

  Enzymes are molecules that have an active site which is complementary to the substrate. The substrate exactly fits into the enzymes, active site. This lowers the activation energy needed to make the reaction react, and then releases the products the enzyme is reusable and not changed so it's free to bump into more substrates and repeat
• Is the volume of product made the same

  Yes, because the quantity of the reactant particles is not increased
• How does a catalyst change the rate of reaction?

  The graph is steeper because the rate is faster since the activation energy is less

  the catalyst lowers the activation energy meaning that there are more successful collisions
• Why are catalysts so important in the chemical industry?


  The same amount of product can be made in a shorter time

  catalyst allow the reaction to take place at a good rate at a lower temperature thus less energy is needed for the reaction. This means that less fuels are burned, and there's less pollution and decreasing costs.
• What are enzymes?

  Proteins, which catalyze bio chemical reactions, taking place in cells
• What substances can be used as catalysts


  Very often transition metals and their compounds are good catalysts for various reactions
• Describe an experiment to show that the catalyst manganese dioxide does not get used up when it catalyzes the decomposition of hydrogen peroxide

  Do the reaction the first time with 5 g of manganese oxide

  filter the solution so you get manganese oxide as a residue in the filter paper and water as your filtrate let it dry and then measure the mass. It should be the same if it's not used up 5 g do the reaction again with a fresh batch of hydrogen peroxide this proves that chemically the manganese oxide is not any different
• Does catalyst affect delta H?

  No there's no difference in Delta H
• How does a catalyst work?


  Mac Catalyst makes the reaction go by a different pathway where weaker bones are broken so the reaction has a lower activation energy
• The catalyst produce more product


  Catalyst never produce more product they make the same amount of product in a shorter time and using less energy
• What is a catalyst?

  Are substances that increase the rate of a reaction without themselves getting used up
• Is the volume of products made the same,

  No, it is more because there's more of both reactants to be used
• What will happen to the rate of reaction if the concentration of both reactants is increased?

  The graph is steeper, because there is more of both reactants, so more particles and more successful collisions and the rate of reaction increases
• Is the volume of product made the same?

  Yes, the mass of the other reactants limits The amount of product made

  the increased reactant is in excess you have more than you need

  there isn't enough of the other reactant to bond with it
• What will happen to the rate of reaction if the concentration of a reactant is increased?

  The graph is steeper because there's more reactant so more particles in the reactants so more collisions and successful collisions and the rate of reaction increases
• Is the volume of product made the same

  Yes, because the mass of the reactants have not been changed
• What happens the rate of the reaction when one reactant is changed to a powder form?

  The graph is steeper, because there is a greater surface area so more particles, so more successful collisions with the reactants, and the rate of reaction increases
• Is the volume a product made the same

  Yes, because the mass of the two reactants have not been changed
• What happens if a reaction is done at a higher temperature?

  The graph steeper, because there are many particles moving fast with energy some more successful collisions between the reactants in the rate of reaction increases
• When will the reaction stop?

  When one of the reactants is completely used up, the reaction will stop because there will be no more collisions between reactants
• What is the relationship between surface area of solids and rate of reaction?

  The larger the surface area, the higher the rate of reaction since there are more particles, so more collisions and more successful collisions to the rate of reaction increases
• After the reaction stops the line horizontal will there be an increase in the volume of product produced?

  It would stay the same because at that time all of the reactions would still have been used up

  no more product would have been produced.
• How does the rate of reaction change over time and why does the rate change like this?

  Rate of reaction decreases as the reaction proceeds until it stops. There is not rate

  at the start of the reaction there are more particles particles (higher concentration of the reactants) so more collisions between particles

  reactant particles get used up lowering concentration, so there are fewer collisions between reactant particles, and fewer successful ones, so that the rate slows
• Why does the reaction stop?

  One or both reactants are finished
• Why does the rate of reaction slow down over time?

  In the beginning, you have lots of magnesium particles higher concentration. They are bumping together often and some of these collisions are successful as they react the particles are being used up turning into products, so there are fewer of them ;lower and lower concentration. This means we have fewer and fewer successful collisions so reactions slows down
• What happens if the rate of reaction is fast In terms of time?

  The faster than reaction the less time it takes for the reaction to finish, therefore the higher the rate of reaction
• How does a diagram show the rate of reaction?

  There is a steep gradient at first, then a less steep gradient and then the graph goes flat end of reaction
• What do reactions that happen quickly have in terms of activation energies

  Reactions that happens quickly have a little activation energies

  a little of energy is needed to break bonds to start off the reaction
• What do reactions that happens so they have in terms of activation energy?

  Reactions that happen slowly have high activation energies. A lot of energy is needed to break bonds to start off the reaction.
• Why are refrigerators an important invention?

  It slows down the reaction in bacteria and other micro organisms that rot food and slows down the enzymes that help catalyze the metabolic reactions
• By how much temperature rise does the rate of reaction increase?

  A general rule is that for every 10°C rise in temperature the rate of reaction increases
• Why does high temperature make a rate of reaction go faster?

  At higher temperatures, the particles have more kinetic energy so move faster thus the particles will collide more often also at a higher temperature, all the particles move faster, but there's a higher percentage of particles that have enough energy to break bonds when they collide so at higher temperatures, there are more successful collisions.
• How do particles move at low temperature?

  They move slower
• How do particles move at high temperature?

  They move faster
• Why is it dangerous for coal miners to use naked flames while mining?

  Powder from the coal has a high surface area, so can easily ignite with a naked flame and react with the oxygen in the air. The reaction would be very fast and exothermic, so explosive. Also gases that are released have a high surface area and these are flammable, so can combust the reaction is exothermic and very fast —>explosive.
• Why do powdered solids easily ignite when they come into contact with sparks?

  Powdered solids have a large surface area so the rates of reaction are very fast. A spark can be enough to reach activation, energy and get the combustion reaction started

  once started It goes fast releasing heat energy that is explosive.
• How do you make a solid have a high surface area?

  By breaking it, up into as many pieces, or by making it into a fine powder
• Low surface area


  Fewer particles exposed per volume of solid

  Fewer collisions per second