Rates of reaction topic 7

• When do reactions occur

  When particles colliding and rate of reaction are increased when frequency and/or energy of collision is increased
• Catalyst is substance that:

  • Increase rate of reaction
  • Don't alter products of reaction
  • Is unchanged chemically and in mass at end of the reaction
• What amount of mass of catalyst needed to increase rate of reaction


  Small mass
• When using graphs for rate of reaction what do you plot when anylasing?


  Graph of moss or volume of product against time
• On graph what does gradient =


  Rate of reaction
• Steeper the line = greater rate of reaction
• What are enzymes?


  Biological catalysts which can control reactions in cell
• what do particles need to collide with for chemical reaction to happen

  Correct energy
• Activation energy 


  Minimum energy needed for reaction
• Rate=


  Amount of product formed/time taken
• What 5 things increase rate of reaction?

  Surface area, concentration, pressure, catalyst, tempature
• How does tempature increase rate of reaction

  Increase tempature and reactant particles gain kinetic energy so particles collide with more energy often
• How does smaller pieces (surface area)increase rate of reactions?

  Have more surface area to volume ratio so more space for other reactant particles to collide so more frequent collisions and more reactions happen faster
• How does concentration increase rate of reaction?

  More particles in same space so particles are closer toghether and more frequent collisions
• How does pressure increase rate of reaction?

  More reactant particles close toghether so more frequent collisions
• How does catalyst increase rate of reaction?

  Low activation energy so frequent successful collisions
• Steeper the tangent the faster the reaction
• How to calculate tangen(rate of reaction)on graph

  Turn into triangle and divide height by width
• Exothermic

  • Makes bonds
  • Gives out heat energy so tempature increase
• Endothermic

  • Breaks bonds
  • Takes in energy so surroundings decrease
• Examples of exothermic?


  Neutralisation,displacement and combustion
• Examples of endothermic?


  Reaction between citric acid and sodium hydrocarbonate,thermal decomposition
• Some slats can be dissolved in water to be endothermic or exothermic
• What is bond energy?

  Energy needed to break bond or energy related when bond forms
• Exothermic has negative energy change

  Endothermic has positive change
• exothermic if more heat energy is released in forming bonds in the products than is required in breaking bonds in the reactants
• endothermic if less heat energy is released in forming bonds in the products than is required in breaking bonds in the reactant
• Bond energy measure in kJ mol^-1
• Exothermic reaction 


  Products at low level than reactants

  
• Endothermic 


  Products at high energy level than reactants

  
• Rate = reactants used/time
• Quicker gas is = faster rate of reaction
• How do you collect gas if reaction produces gas

  using a gas syringe or an upside-down measuring cylinder.
• It's important that no gas escapes, so the apparatus should be sealed using bungs and tubes.