Random Chem

• What is a colorimeter?


  Instrument for measuring the absorbance of light through a solution.
• How can half life be used to determine the order of a reaction?

  If the half life is constant then its a first order reaction.
• How can k be determined from half life?

  K=ln2/half life.
• Why does k get smaller as activation energy increase?

  Negative fractional power gets larger so smaller fraction. A large activation energy also means a slower rate as less particles have sufficient energy to react (maxwell-boltzman).
• Why does k rise as temperature increases.

  If T increases, negative fractional power decrease, so larger Ea. High temp. means more particles have sufficient energy to react.
• What do conjugate species differ by?

  A proton (H)
• What is the enthalpy change of formation?Exo or Endo?

  Enthalpy change when one mole of a substance is formed from its constituent elements with all substances in their standard forms. Exothermic
• What is enthalpy change of combustion? Exo or Endo?

  Enthalpy change when one mole of a substance undergoes complete combustion in oxygen with all substances in standard states. Exothermic
• What is enthalpy change of neutralisation? Exo or endo?


  Enthalpy change when one mole of water is formed in a reaction between an acid and an alkali under standard conditions. Exothermic.
• What is ionisation enthalpy?Exo or Endo?


  Enthalpy change when one mole of electrons is removed from a gaseous atom/1+ion to produce on mole of gaseous 1+/2+ ions. Endothermic
• What is electron affinity?

  Enthalpy change when each atom in one mole of gaseous atoms gains an electron to form negative ions.
• What is enthalpy of atomisation? Exo or endo?

  Enthalpy change when one mole of gaseous atoms is produced from an element in its standard states. Endothermic
• What is hydration enthalpy? Exo or endo?

  Enthalpy change when one mole of gaseous ions become hydrated (dissolved in water). Exothermic
• Why is 2nd electron affinity endothermic when 1st electron affinity is exothermic?

  Negative electrons are being added to a negative ion so repulsion occurs.
• What is enthalpy change of solution? Exo or endo?

  Enthalpy change when one mole of an ionic solid dissolves in an amount of water large enough so that the dissolved ions are well separated and do not interact with each other. Can be both exothermic and endothermic.
• What is bond dissociation enthalpy? Exo or endo?

  Enthalpy change when one mole of covalent bonds is broken in the gaseous state. Endothermic.
• What is lattice enthalpy of formation? Exo or endo?

  Enthalpy change when one mole of a solid ionic compound is formed from its constituent ions in the gas phase. Exothermic.
• What is lattice enthalpy of dissociation? Exo or endo?

  Enthalpy change when one mole of a solid ionic compound is broken up into its constituent ions in the gas phase. Endothermic.
• What is enthalpy change of vaporisation? Exo or endo?

  Enthalpy change when one mole of a liquid is turned into a gas. Endothermic.
• What is enthalpy change of fusion? Exo or endo?

  Enthalpy change when one mole of a solid is turned into a liquid. Endothermic
• What is entropy?


  A measure of the disorder in a system.
• What state has the highest entropy?

  Gas
• Does increasing moles increase or decrease entropy?

  Increase
• What is gibbs free energy change?

  A measure used to predict if a reaction is feasible (spontaneous).
• What value of ΔG shows feasibility?

  Negative
• What does feasibility depend on?

  Temperature
• Why is starch added to the end of iodine titrations?

  To determine the end point. Starch is blue/black in I2 and Colourless in I-.
• What is an electrochemical cell?

  A store of chemical energy in a closed system
• What is a fuel cell?

  An electrochemical device that converts chemical energy into electrical energy, in an open system.
• What do fuel cells require?

  A fuel (often hydrogen)and an oxidant (often oxygen)
• What are the two main methods of manufacturing hydrogen?

  Reaction of hydrocarbons with steam (CO2 by product) or electrolysis of acidified water.
• How can hydrogen be stored?

  As a liquid under pressure (must be kept cold), absorbed within materials or adsorbed onto the surface of materials.
• What is Boyles Law (pressure and volume)?

  The higher the pressure, the lower the volume at a fixed temperature.
• What is Charles Law?

  The volume of a fixed mass of a gas (at a fixed pressure) is proportional to its absolute temperature.
• What is Avogadro's principle?

  The volume of a gas is proportional to the number of moles of gases.
• What are the kinetic theory assumptions about ideal gas?

  Gases are made up of molecules which are in constant random motion.

  Molecules behave as rigid spheres

  Pressure is due to collisions between molecules and walls if the container.

  Temperature of a gas is proportional to average kinetic energy of the molecules.
• What is a catalyst?


  A substance that lowers the activation energy of a reaction without without being used up, by providing an alternative pathway. This speeds up the rate of reaction.
• What is dynamic equilibria?

  When both the forward and reverse reaction occur at the same rate in a closed system. The concentration of products and reactants remains constant.
• What is le chateliers principle?

  If a condition of an equilibrium is changed then the position of the equilibrium will shift to counteract the change.
• What does a Kc of 1 mean?

  Equal products and reactants.