enthalpy

• exothermic is the release of heat.
• exothermic makes bonds
• exothermic has a negative enthalpy change and increases in temperature
• endothermic is the absorption of heat.
• endothermic breaks bonds
• endothermic has a positive enthalpy change and decreases in temperature
• calorimetry 1 - take start temp of reactants, mix together, take end temp
• calorimetry 1 - put beaker in polystyrene cup with cotton wool = insulator to stop heat loss
• calorimetry 2 - 50cm3 of water and take start temp, weigh the burner and lid, heat to 50* and weigh the burner and lid again, calculate the mass of fuel used and energy change
• calorimetry 2 - use a copper pot and lid = stops heat loss to surroundings
• Q=mc^t - energy change=mass of water x 4.2 x temperature change
• ^H=-Q/moles —— enthalpy change = - heat energy change / moles
• bonds = total energy taken in - total energy taken out
• exothermic diagram - starts high, finishes low = reactants have higher energy level than product, negative enthalpy change
• endothermic diagram - starts low, finishes high = reactants have lower energy level than product - positive enthalpy change
• catalyst reaction = increases rate of reaction by lowering activation energy (provides alternate route) - weaken the bonds so it’s easier to break them
• endothermic is the breaking of bonds
• exothermic is the making of bonds
• the term endothermic = a reaction in which heat is taken in (surroundings get colder)
• the term exothermic = a reaction where the energy is given out (surroundings get hotter)
• why is the experimental value different to the theoretical value?

  heat energy is lost to the surrounding or not all the reactant is used up
• Q = m x c x Δ x T
• molar enthalpy = kj/mol
• endothermic graph - ΔH = enthalpy change

  
• exothermic graph - ΔH = enthalpy change

  
• exothermic reactions have a negative enthalpy change
• endothermic reactions have a positive enthalpy change
• neutralisation reactions are exothermic
• displacement reactions are exothermic
• combustion reactions are exothermic
• a solid dissolving is endothermic