CHMA10H3 Lecture Notes - Lecture 4: Thermodynamics, Internal Energy

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CHMA10 Lecture 4: Introduction to Thermochemistry
- Heat (q): the flow of thermal energy from one system to the surroundings due to the
temperature difference between them
o Heat flow will stop when the temperatures of the system and the surroundings
are both the same
- Work (w): the force acting through a distance to displace something
- Kinetic Energy: energy associated with motion
o Measured in joules (J)
- Thermal Energy: energy associated with temperature
- Potential Energy: energy associated with position or composition
o Any object that is elevated above a surface stores energy in the form of potential
energy
o When said object is dropped, the potential energy is converted to kinetic energy
o Chemical Energy: a form of potential energy associated with the positions of
electrons and nuclei in a system
- 6.3: Law of Conservation of Energy
o Law of Conservation of Energy: energy cannot be destroyed or created but it
can be transformed into different forms and transferred from one object to
another
o System: a specific area of interest
Eg: a chemical reaction, a boiling pot of water,
o Surroundings: everything around the system
Any energy lost by the system is gained by the surroundings and vice
versa
o First Law of Thermodynamics: The total energy of the universe is constant
Thermodynamics: the general study of energy and its conversions
o Internal Energy (U): sum of kinetic and potential energy of a system, is a state
function
U = Ukinetic + Upotential
The reactants and products themselves do not change
However the pathway from the reactants to the products can
change
The internal energy of the reactants and products will always
remain the same regardless of the path taken
o This is why Internal energy can be classified as a state
function
State Function: measurements that only depend on the initial and final
states, not on the actual process
Change in internal energy of a system can be defined in terms of heat and
work
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Document Summary

Heat (q): the flow of thermal energy from one system to the surroundings due to the temperature difference between them: heat flow will stop when the temperatures of the system and the surroundings are both the same. Work (w): the force acting through a distance to displace something. Kinetic energy: energy associated with motion: measured in joules (j) U = q + w (it is the sum of heat and work) If delta u is positive: energy is flowing into the system. If delta u is negative: energy is flowing out of the system. If q is positive: the system is gaining thermal energy. If q is negative: the system is losing thermal energy. If w is positive: work is being done on the system. If w is negative: work is being done by the system: analyzing energy flow in 2 different reactions, 1: when the reactants have higher internal energy than the products.

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