Chemistry lecture 11

• ORGANIZER


  • ENERGY BASIS FOR ACTION
  • HEAT ENERGY
  • POTENTIAL ENERGY
  • KINETIC ENERGY
• Energy


  Something an object has if the object is able to do work. It is the ability to do work.
• Types of energy


  • Kinetic Energy (KE)
  • Potential Energy (PE)
• Kinetic Energy (KE)


  The energy an object has when it is moving. It depends on mass & velocity.
• Potential Energy (PE)


  The energy an object has due to its position with respect to height or ability to attract or repel.
• How to increase Potential Energy

  1. When objects that attract each other are pulled apart there is an increase in their potential energy.

  2. When objects that repel are forced closer their potential energy also increases.
• How to decrease Potential Energy


  1. 1.When objects that attract each other are brought closer to each other their potential energy decreases.

  2. When objects that repel are moved apart their potential energy also decreases.
• Molecules in Solids, Liquids & Gases have the same average kinetic energy at the same temperature, but different Potential energies!
• Heat (q)


  A form of kinetic energy associated with the random motion of the elementary particles in matter.
• Heat capacity


  The amount of heat needed to raise the temperature of a defined amount of a pure substance by one degree.
• Molecules in Solids, Liquids & Gases have the same average kinetic energy at the same temperature, but different Potential energies
• Kinetic theory of heat

  Based upon the kinetic molecular theory. The average kinetic energy of a collection of gas particles is dependent only upon the temperature of the gas.
• In principle, if a reaction gives off energy, the products formed must have lower energy and be lighter than the reactants.
• However consider a release of 100 kcal by a typical chemical Reaction. This energy corresponds (via the Einstein relationship) to a mass loss equivalent to one hundred thousandth(1/100,000) the mass of an electron (1/100,000 of 9.31 x 10-31kg). This amounts is far less than we can measure. Thus we can say that, for chemical reactions, mass(m) and energy (E) are conserved independently.
• Effect of Catalyst


  The catalyst lowers the activation energy allowing more particles to form products.
• Thermochemistry


  A branch of thermodynamics which focuses on the study of heat given off or absorbed in a chemical reaction.
• Temperature


  An intensive property of matter; a quantitative measurement of the degree to which an object is either "hot" or "cold".
• Temperature scales


  • Fahrenheit
  • Celsius (centigrade)
  • Kelvin
• Heat (q)


  A form of energy associated with the random motion of the elementary particles in matter
• Specific heat


  The amount of heat needed to raise the temperature of one gram of a substance by 1 ℃ (or 1 K)
• Molar heat capacity


  The amount of heat required to raise the temperature of one mole of a substance by 1 C (or 1 K)
• Sensible heat


  Heat that can be detected by a change in the temperature of a system.
• Latent heat


  Heat that cannot be detected because there is no change in temperature of the system.
• Examples of latent heat


  • The heat that is used to melt ice or to evaporate water is latent heat.
• Forms of latent heat

  • Heat of fusion
  • Heat of vaporization
• Heat of fusion


  The heat that must be absorbed to melt a mole of a solid.
• Heat of vaporization


  The heat that must be absorbed to boil a mole of a liquid.
• A typical thermochemical equation: H2(g) + 0.5 O2(g) → H2O(l) ΔH = -285kJ @ STP
• Properties of thermochemical equation

  • -balanced for charge/mass
  • -states & sign of ΔH shown
  • -ΔH increase by same factor as equation
• Enthalpy of Reaction (rHº)

  Change (Δ) in enthalpy (H) during a chemical reaction (r) where the mole quantities of the chemicals and their states are specified by the reaction equation
• Standard Enthalpy of Formation (fHº)

  Energy released or absorbed when one mole of product is formed from its constituents at STP
• Standard Enthalpy of Combustion (cHº)

  Energy released when one mole of a substance is completely burnt in oxygen at STP
• Do tutorial 2.6 questions in study guide
• EXPERIMENT 6a Heats of Reaction