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Lesson 8 - Thermodynamics - Coggle Diagram
Lesson 8 - Thermodynamics
Thermodynamics is the study of the transformation of energy.
The term "thermo" means temperature, thermal, heat, and energy.
The term "dynamics" means motion.
The first law of thermodynamics: energy can be converted from one form to another but cannot be created or destroyed.
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Some examples are electrical energy can be converted to heat, chemical energy can be converted to light.
Enthalpy
Enthalpy change (∆H) is the amount of heat released or absorbed by a chemical system when a chemical reaction occurs at constant pressure.
Endothermic reaction
Heat abosrbed from surroundings
∆H positive
Products have more energy than reactants
Exothermic reaction
Products have lesser energy than reactants
Heat released to the surroundings
∆H negative
Standard enthalpy change
The standard enthalpy change for a reaction or physical process (ΔH°) is the enthalpy difference between the products in standard state and the reactants in standard state, at the same specified temperature.
For example, the standard enthalpy of vaporization (ΔvapH°) of water is the enthalpy change per mole when a pure water at 1 bar vaporizes to a gas at 1 bar.
Standard state
The standard state of a substance at a specified temperature is its pure form at 1 bar.
For example, standard state of ethanol at 298K, 1 bar is liquid.
Note: 298 K = 25 °C
Standard Enthalpy of Formation (∆fH°)
The standard enthalpy of formation of an element is zero.
∆fH° (C) = 0 kJ/mol
Other than monoatomic elements such as carbon, sodium, and zinc, there are also seven diatomic elements (H2, N2, O2, F2, Cl2, Br2 and I2).
The seven diatomic elements are also zero. Example: ∆fH°(Cl2) = 0 kJ/mol
Standard enthalpy of transition
standard enthalpy change that accompanies a change in physical state
Hess's Law
Hess‘s Law states that the heat evolved or absorbed in a chemical process is the same whether the process takes place in one or multiple steps.
Hess’s Law can be represented in two different diagram forms
Energy cycle diagram
Energy level diagram
The second law of thermodynamics: a physical law based on universal experience concerning heat and energy interconversions/direction of natural process
The transfer of heat goes from hot to cold, heat will not flow spontaneously from a cold object to a hot object
The Third Law of Thermodynamics: a perfect crystal at zero Kelvin (absolute zero) has zero entropy
Freezing a block of ice to a colder and colder temperature will slow down its internal molecular motions more and more until they reach the least disordered state
standard Enthalpy transition :- change that acamponies change in physical state.