Thermochemistry

• Low speed = low temp = low kinetic energy
• When energy is added, attractions are broken
• When energy is removed, attractions are formed
• Attractions between phase changes are called intermolecular forces
• Intermolecular forces = the attractions between molecules in a substance
• IMFs can affect boiling point of substance
• Endothermic = phase changes absorb energy
• Exothermic = phase changes release energy
• Sublimation = S->G
• Vaporization = L->G
• Melting = S->L
• Deposition = G->S
• Condensation = G->L
• Freezing = L->S
• Evaporation = occurs only at surface

  Atmospheric pressure > vapor pressure
• Boiling = occurs throughout liquid

  Atmospheric pressure = vapor pressure
• Temperature and pressure control the phase of substance
• Specific heat (c) = how much heat a substance can absorb
• High specific heat = small change in temp. of the substance
• Water has the highest specific heat capacity of any liquid or solid
• Higher specific heat = absorbs more heat
• Specific heat = Intensive property
• Insulator prevents heat transfer
• Conductor allows heat transfer
• Calorimeters are used to measure the amount of heat transferred in physical and chemical changes
• If two objects are the same temp. , they are in thermal equilibrium and no heat flows from one to the other
• Conduction is the transfer or heat through direct contact
• Convection is the transfer of heat through liquid or gas
• Conductors allow current to flow through it; low specific heat capacity (c)
• Insulators don't allow current to flow through it; high specific heat capacity
• Heat transfers from hot to cold
• Energy in an endothermic reaction is absorbed
• Energy in an exothermic reaction is released
• An endothermic reaction feels cold
• Enthalpy is the transfer of energy within reaction in the form of heat
• Activation energy is the minimum amount of energy needed to start a reaction.
• A catalyst is a substance that speeds up a reaction and lowers activation energy