Chapter 6 Thermochemistry Intro Presentation

The Nature of Energy Energy is the capacity to do work or to produce heat through a process In chemistry we are concerned with the heat transfer that occurs during chemical reactions Heat/Energy flows from high to low concentration The energy of the universe is constant (Law of Conservation of Energy)

Law of Conservation of Energy Energy cannot be created or destroyed, only converted from one form to another via reactions and processes Energy is classified as either kinetic or potential

Potential Energy Energy due to position or composition Potential energy is able to be converted to work when it is being used

Kinetic Energy Energy due to the motion of the object Depends on the mass of the object and its velocity Energy is able to be converted from one form (potential) to the other (kinetic) Always remember Temperature is a measurement of the randomness of a particle and is not the same thing as Heat.

Two Ways To Transfer Energy 1. Heat– involves the transfer of energy between two objects due to a difference in temperature Does not refer to a substance that is contained by an object Moves from high to low

Work Force acting over a distance PE is transferred through work from one object to another So we have two ways to transfer energy, heat and work

Energy is a State Function A state function/property is one that depends only on the present state of the system This means it does not depend on the past/future of the object A change in the function (property) in going from one state to another is independent of the pathway taken between the two states

Work and Heat are NOT State Functions Energy and enthalpy are Energy changes are independent of the pathway taken because no matter what, the measured value is always the same Work and heat are dependent on the pathway that we take

Chemical Energy 1. System– Part of the universe that we wish to focus our attention on Example: Products and reactants 2. Surroundings—Everything else in the universe Example: Container the reaction takes place in In chemistry we always take the SYSTEMS point of view

Exothermic Process Any reaction that involves the flow of energy/heat out of the system From system to surroundings Represented by a negative sign

Endothermic Processes Any reaction that involves the flow of heat/energy in to the system From surroundings into system Use a positive sign to indicate that any process is endothermic

First Law of Thermodynamics States that the energy of the universe is constant Basically this law is the law of conservation of energy According to this law, the amount of heat lost in any process should equal the amount of heat gained by some object related to the process

Internal Energy Sum of KE and PE equals the internal energy (E) of the system In the equation, the sign reflects the systems point of view If the system works on the surroundings w is (-) because work flows out of system If the surrounding are working on the system w is (+) because energy will flow into the system

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