Reaction Energy and Reaction Kinetics Chapter 17 Notes

Thermochemistry Thermochemistry is the study of the transfers of energy as heat that accompany chemical reactions and physical changes. – Endothermic and exothermic reactions – Phase changes and specific heat

Calorimeter The energy absorbed or released as heat in a chemical or physical change is measured in a calorimeter.

Heat and Temperature Heat (q): energy transferred between samples of matter because of a difference in their temperatures. Temperature: a measure of the average kinetic energy of the particles in a sample of matter. – Higher temperature = faster particles – Lower temperature = slower particles

Heat As an object absorbs heat – the particles increase in kinetic energy – the temperature of the object increases Heat always flows from a __________object to a __________ object hotter colder

Thermochemical Systems System: the collection of matter that you are studying – The liquid in which a reaction is taking place – The interior of a calorimeter Surroundings: the area directly around the system that is capable of absorbing energy from or releasing energy to your system – The beaker holding the liquid and the air around the beaker – The walls of the calorimeter and the air around them

Law of Conservation of Energy Energy cannot be created or destroyed. It can be moved from place to place

Endothermic Process An endothermic process absorbs heat from its surroundings – Instant cold packs – Vinegar and baking soda – Boiling water

Exothermic Process A system that releases energy to its surroundings – Diluting sulfuric acid – Water freezing into ice – The heating unit included in MREs

Heat of Reaction The energy transferred as heat during a chemical reaction is called the heat of reaction. This heat is shown as either a reactant or a product in a thermochemical equation. CH O 2 → CO H 2 O J CH 3 COOH + NaHCO J → NaC 2 H 3 O 2 + CO 2 + H 2 O Exothermic Endothermic

Enthalpy Enthalpy change: the amount of energy transferred as heat during a process occurring at constant pressure ΔH = H products – H reactants – Positive for endothermic reactions – Negative for exothermic reactions

Enthalpy and Thermochemical Equations Exothermic reaction CH O 2 → CO H 2 O J ΔH J Endothermic reaction CH 3 COOH + NaHCO J → NaC 2 H 3 O 2 + CO 2 + H 2 O ΔH = J

Entropy Entropy: the amount of disorder within a system – High entropy = chaotic The plasma inside the sun Typical kid’s bedroom – Low entropy = very orderly Ice My movie collection Processes occur spontaneously (without an external driving force) if they increase the entropy of the system.