THERMOCHEMISTRY


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Law of Conservation of Energy: the total energy of the universe is constant and can neither be created nor destroyed; it can only be transformed.

The internal energy, U, of a sample is the sum of all the kinetic and potential energies of all the atoms and molecules in a sample
i.e. it is the total energy of all the atoms and molecules in a sample

Systems & Surroundings
In thermodynamics, the world is divided into a system and its surroundings
A system is the part of the world we want to study (e.g. a reaction mixture in a flask)
The surroundings consist of everything else outside the system
OPEN SYSTEM: can exchange both matter and energy with the surroundings (e.g. open reaction flask, rocket engine)
CLOSED SYSTEM: can exchange only energy with the surroundings (matter remains fixed) e.g. a sealed reaction flask
ISOLATED SYSTEM: can exchange neither energy nor matter with its surroundings (e.g. a thermos flask)

HEAT and WORK

HEAT is the energy that transfers from one object to another when the two things are at different temperatures and in some kind of contact
e.g. kettle heats on a gas flame
cup of tea cools down (loses energy as heat)