Chemistry

• reaction rate = change in quantity of reactant or product / time interval
• Rate of reaction at the start of the reaction is very high
• The graph shows that the reaction begins very quickly and the rate then decreases until it becomes unchanging and CO2 is formed at a constant rate. At this stage, the reaction is at equilibrium.
• In collision theory, the reactant particles must collide
• In collision theory, the reacting particles must collide with sufficient energy. Reactants must have enough activation energy
• In collision theory, on collision, the particles must have the correct orientation.
• For an exothermic reaction:

  • the products have less potential energy than the reactants

  • heat energy is released and an increase in the temperature of the surroundings occurs

  • the heat of reaction (∆H) For an exothermic reaction has a negative value
• For an endothermic reaction:

  • the products have more potential energy than the reactants

  •∆ H is positive

  • heat energy is absorbed from the surroundings and as a result a decrease in the temperature of the surroundings occurs
• To increase the Rate of reaction:

  Higher concentrations result in more frequent collisions between reactant particles
• •To increase the Rate of Reaction:

  Have reactants that are finely divided – increased surface area results in more frequent collisions between particles
• •To increase the Rate of Reaction:

  When the temperature increases, the average kinetic energy and the frequency of collisions would increase. More particles will also have the required activation energy therefore particles undergo more successful collisions.
• •To increase the Rate of Reaction:

  Catalysts provide a pathway that reduces the activation energy and make it easier for particles to react, resulting in more successful collisions.
• To increase the Rate of Reaction: (in terms of it's nature)

  Need less bonds to be broken or weaker bonds to be broken. If strong bonds need to be broken, the reaction is slow.
• The equilibrium constant (K) has a constant value at a particular temperature and is usually expressed at 25 °C
• When writing equalibirum law expressions:

  • Concentrations of the products are on the top and the concentration of reactants are on the bottom line

  • Reactants or products are multiplied together

  • The power of the concentration is their stoichiometric number.

  • Solids and liquids are not included.
• A high K value will favour the products (fast reaction) and a low K value will favour the reactants (slow reaction)
• The equilibrium constant (K) has the following characteristics:

  1. Always positive number
  2. Allows to predict how far an equilibrium reaction will go in one direction.
  3. If the temperature is changed, the K value will change
  4. It provides no indication of the rate of the reaction.
• In a closed system:

  •Forward reaction rate is initially fast, but as the concentrations of the reactants decrease, the forward reaction rate decreases.

  •The rate of this reverse reaction is initially zero as there is no products in the system, but it gradually increases as the concentration of product increases.
• At Equilibrium:

  1.The rates of the forward and reverse reactions are equal.

  2. Equilibrium is dynamic because the reactions are ongoing and are happening at the same time

  3. Reverse and forward reactions are still occurring, at the same rate. As a result, the macroscopic properties such as mass, colour, concentrations of the reactants and products present remain constant but are not the same.
• At physical equilibrium:

  a.The rate at which the liquid is evaporating will equal the rate at which the vapour is condensing.

  b. The amount of liquid ,vapour and the vapour pressure will remain constant.
• At Saturated solution equilibrium:

  1. Rate of dissociation = Rate of  crystallisation
  2. the amount of solid present will remain constant.
• Le Chatelier’s principle states:

  'If a change is made to the system when it is at equilibrium ,the system will partially counteract the imposed change.’
• When the concentration of one of the reactants is increased, the reaction has a shift right and so the concentration of products will gradually increase until it reaches equilibrium once more.
• When the concentration of one of the reactants is decreased, the reaction has a shift left and so the concentration of reactants will gradually increase until it reaches eqilibrium once more.
• For gaseous systems, an increase in pressure will favour the side of the reaction with the least number of particles
• The equilibrium of a gaseous system is unaffected by the addition of an inert gas
• For reactions occuring in a solution, diluting the solution will favour the side of the reaction with the most number of particles
• To figure out the effect temperature has on the reaction, look at which side the energy is on. Endothermic is reactant side (positive). Exothermic is product side (negative)
• The addition of a catalyst shifts the reaction neither direction, only affecting how quickly equilibrium is attained.
• CO2(g) -><- CO2(aq)

  CO2(aq) + H2O(l) -><- H2CO3(aq)

  H2CO3(aq) + H2O(l) -><- H3O+(aq) + HCO3-(aq)

  HCO3-(aq) + H2O(l) -><- H3)+(aq) + CO3 2-(aq)

  A) CO2