Intro to energy

• Energy


  The capacity to perform work
• Kinetic energy


  Energy related to the motion of an object or particles
• Potential energy


  Energy stored in an object or system of particles due to its position or arrangement of parts
• Thermodynamics

  • The study of energy
  • The First Law of Thermodynamics states that energy cannot be created or destroyed, and the amount of energy in the universe is constant (Law of Conservation of Energy)
  • During any chemical or physical process, all the energy can always be accounted for
  • Energy can be transferred from one system to another, or it can be transformed from one type of energy to another type of energy
• In all energy transfers and transformations, some energy is "lost" as heat that is released to the surrounding
• Heat always transfers from warmer temperature objects to cooler temperature objects
• The temperature of a substance increases when heat energy is transferred to it, because the particles within the substance will move faster
• A hot metal block that is exactly the same size as a cold metal block will have a higher amount of thermal energy
• Temperature


  A measure of the average kinetic energy of the particles that make up a substance/object
• Thermal energy


  The total combined kinetic energies of all the moving particles that make up a substance/object
• Heat

  The energy that transfers from one object to another because of temperature differences between them
• Heat always flows from a warmer temperature object to a cooler temperature object, until the temperature of both objects is the same (thermal equilibrium)
• The larger block will have more thermal energy after reaching thermal equilibrium, because it has more mass and therefore more moving particles
• Types of heat transfer

  • Conduction
  • Convection
  • Radiation
• Water boiling is endothermic because the system (water) is absorbing energy from the surrounding (the stove)
• Liquid water freezes into ice when placed in a freezer

  1. Liquid water molecules have less kinetic energy than the air inside the freezer

  2. Energy from the air is transferred to the water

  3. This causes the liquid water molecules to lose energy and become a solid

  4. Water freezing is an endothermic process
• Chemical reactions and changes in states of matter involve either an absorption or release of energy (usually in the form of heat)
• System


  The chemical reaction that is taking place or a substance involved in a phase change
• Surrounding


  The immediate area around which the chemical reaction or phase change is taking place
• Endothermic process

  The system absorbs heat from its surrounding, causing the surrounding to cool down
• Exothermic process

  The system releases energy to its surrounding, causing the surrounding to heat up
• States of matter and phase changes

  • Substances in the solid state have the lowest amount of kinetic energy, substances in the liquid state have more kinetic energy than solids, and substances in the gaseous state have the most kinetic energy
  • Substances can undergo phase changes by releasing or absorbing heat energy
• Exothermic phase changes

  • Freezing
  • Condensing
  • Deposition
• Endothermic phase changes


  • Melting
  • Boiling/Evaporation
  • Sublimation
• In endothermic reactions, the products have more potential energy than the reactants
• In exothermic reactions, the reactants have more potential energy than the products
• Endothermic reactions have a positive change in enthalpy
• Exothermic reactions have a negative change in enthalpy
• In endothermic reactions, more energy is required to break bonds than energy is released when bonds form
• In exothermic reactions, more energy is released when bonds form than energy is required to break bonds
• Exothermic reactions release heat energy to the surrounding
• Endothermic reactions absorb heat energy from the surrounding
• In endothermic reactions, the surrounding cools down
• In exothermic reactions, the surrounding heats up
• During a chemical reaction, the atoms in chemical substances (the reactants) are rearranged to form new substances (the products)
• Energy is absorbed (or required) when bonds break, and energy is released when new bonds form
• Change in enthalpy (ΔH)


  The net (overall) change in energy that takes place during a reaction
• Activation energy (EA)


  The initial amount of energy that the reactants need to absorb in order for bonds to start breaking
• Reactions cannot occur unless the reactants absorb the activation energy required for that reaction
• In exothermic reactions, the potential energy stored in the products is less than the potential energy that was stored in the reactants