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AS and A Level: Physical Chemistry

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The dynamic equilibrium and 'Le Chatelier Principle'

  1. 1 Le Chatelier Principle states “If a system that is in dynamic equilibrium is subjected to a change, the position of equilibrium will shift to minimise that change”. Put simply- if you do something, the system will try and reverse what you’ve done!
  2. 2 Adding a catalyst does not change the concentration, pressure or temperature of a system. Therefore adding a catalyst has no effect on the position of equilibrium.
  3. 3 If you increase the concentration of one side of an equation, the position of equilibrium will shift to the other side (to try and return the concentration back to its original value).
  4. 4 If you increase the pressure of the system, the position of equilibrium will shift to the side of the reaction with less moles of gas (to try and reduce the pressure back to its original value).
  5. 5 If you increase the temperature the position of equilibrium will shift in the direction of the endothermic reaction (to try and reduce the temperature back to its original value).

Top equations for acid / base chemistry (A level only)

  1. 1 For a strong acid the acid concentration is equal to the H+ concentration. This is because strong acids fully dissociate their H+ ions. [acid] = [H+]
  2. 2 For a weak acid, because they only partially dissociate their H+ ions, to find the H+ concentration we must use the following equation: [H+] = √ka[acid]
  3. 3 For a buffer, we calculate the value of H+ by using: [H+] = Ka[acid] / [salt] (where Ka is the acid dissociation constant)
  4. 4 For a strong base, we calculate the H+ value by using: [H+] = Kw / [base] (where Kw is the ionic product of water = 1 x 10-14)
  5. 5 To convert [H+] into pH, we would use the equation: pH = -log[H+]

Top tips for ionisation energy

  1. 1 One of the factors which will affect ionisation energy is electron shielding. This is how many inner shell electrons an atom has. The more electron shielding, the lower the ionisation energy. Electron shielding stays the same across a period and increases down a group.
  2. 2 The second factor affecting ionisation energy is the proton number / nuclear charge. The higher the nuclear charge the higher the ionisation energy. Nuclear charge increases across a period and down a group.
  3. 3 The third factor affecting ionisation energy is the atomic radius (size of the atom). The higher the atomic radius the lower the ionisation energy. Atomic radius decreases across a period (as the increased number of protons pulls the electron shells closer) and increases down a group.
  4. 4 All three of these factors combine to have an effect of increasing the ionisation energy as we go across a period (eg F has a higher ionisation energy than O)
  5. 5 All three of these factors combine to have an effect of decreasing ionisation energy as we go down a group (eg K has a lower ionisation energy than Na)

  • Marked by Teachers essays 14
  • Peer Reviewed essays 19
  1. Experiment to demonstrate the effects of buffers on ph changes.

    However, a weak acid is one that does not completely dissociate or ionize, in a solution. ________________ 3.0 Introduction: Introduction: Mainly, the purpose of this lab is to demonstrate the power and importance of buffer sin regulating the pH of solutions, by adding very small amounts of acid or base to different buffer solutions. Students were able to calculate the buffer capacities of those solutions and some general trends with regard to buffer strength with regards to acid/base balance. Furthermore, the buffer capacity ?, is important in evaluating the buffers used in the lab. The buffer capacity is calculated using the equation below: - In this equation ? represent that the buffer capacity, d[b] and d[a]

    • Word count: 1901
  2. Experiments to examine dynamic equilibrium and Le Chateliers principle

    Le Chatelier's principle describes what happens to a system when something momentarily takes it away from equilibrium. There are three changes that will affect the position of equilibrium momentarily. First, changing the concentration of one of the components of the reaction. Second, changing the pressure on the system. Third, changing the temperature at which the reaction is run. Objectives: Observe the effect of an applied stress on chemical system at equilibrium. A reversible reaction is a reaction in which both the conversion of reactants to products and the conversion of products to reactants occur simultaneously.

    • Word count: 2573
  3. Lab Report. Objectives 1. To determine the enthalpy of neutralization of strong acid and strong base. 2. To determine the quantity and direction of the heat transfer in the dilution of a salt.

    Measure the temperature change, The unit of is kJ/mol of acid and base reacted. Mass (g) of solution is the total mass of acid and base in solution. The enthalpy of solution is produced when a salt dissolve in water. Energy is absorbs and releases. KI dissolves in water : The lattice energy (enthalpy) of salt, and hydration energy (enthalpy), will determined whether heat is absorbed or released when 1 mole of salt dissolve in water. The enthalpy of solution and dilution; is total of and . Salt dispersion enthalpy, is determined experimentally with the combination of heat loss from the salt and water whenever both of them are mixed.

    • Word count: 2807
  4. Assignment 2 M3 Specialist and Non specialist lab

    The science lab will have a first aid kit and eye wash stations. The lab will also have other safety equipment such as fire extinguisher, fire blanket and a sand bucket. This kind of lab would be used by secondary school students to carry out general practicals such as animal dissections, titrations of a chemical and testing electric circuit for voltage and current change. My non-specialist lab has the following equipment: * New fast and efficient computers to be able to do research and type up work * New student benches with integrated gas taps and plug sockets so that they are easily accessible during a practical.

    • Word count: 601

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