CHEM 1050 Lecture Notes - Water Gas, University Of Houston, Zirconium
CHEM*1050 – General Chemistry II
Differential Equations
Differential Equations
Matrix Algebra
Statistica
l
Methods
Calculus
Introduction to THERMODYNAMICS
• science of the interconversion of different forms of ENERGY
e.g
., heat, mechanical work, electrical work, chemical energy, etc
.
• an essential foundation for understanding physical and biological sciences.
• at the centre of any physical description of living matter.
Key Questions:
1. Interconversion of energy – how, why, etc.
2. Is a particular reaction possible?
3. How much useful work can be obtained from a reaction?
4. Can we understand chemical equilibria?
Chemical reactions involve a transfer of energy between
the SYSTEM
and SURROUNDINGS
DEFINITIONS:
SYSTEM – the part of the universe under observation
e.g
., engine, electrical cell, reaction in a flask, etc.
The system can be:
• “Open” – both mass and energy may leave and enter.
e.g.
, beaker
• “Closed” – energy can be exchanged but no mass can enter or leave.
e.g.,
sealed flask
• “Isolated” – neither mass nor energy may enter or leave.
e.g.
, insulated, closed container
SURROUNDINGS – the rest of the universe.
Therefore, the “UNIVERSE” is made up of the “SYSTEM” and the “SURROUNDINGS.
NOTES:
1
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The “state
” of a system is characterised by a set of variables, e.g.
, P, V, T, n, etc.
These are state variables
or state functions
and can be classified as either:
Intensive – independent of size.
e.g.
, P, T, etc.
Extensive – dependent of size.
e.g.
, mass, V, n, etc.
ENERGY TRANSFER
• We can transfer energy in and out of a system, with the result that the
INTERNAL ENERGY
of the system, U, may be changed.
Note: In these notes, U is used to represent the internal energy. Depending on the text,
E or U are commonly used to symbolize the internal energy of a system.
• Internal Energy (U) – sum of all the kinetic (i.e
., movement) energies (KEs) and
potential (i.e
., position/separation) energies (PEs) of the particles within the system.
• Two ways that U can change: heat
(q) and work
(w)
Note: Another way is by adding/removing mass but this is not encountered in a “closed” system.
ENERGY TRANSFER
We can ONLY measure changes in U, not absolute values,
so for any reaction or process, i.e
., Ufinal – Uinitial = U
We can change the internal energy, U, by any combination of q and w.
∴ ΔU = q + w
This is a statement of the conservation of energy:
1st LAW OF THERMODYNAMICS
NOTES:
2
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The Law of Conservation of Energy states energy may be converted from one form
to another but the total quantity of energy remains constant.
HEAT ENERGY, HEAT TRANSFER and TEMPERATURE
U = q + w tells us we cannot create or destroy energy, but it can be
transferred in and out of the system.
TEMPERATURE
– a measure of the particle’s KEs; an indication of heat content
• objects at same T do not exchange heat energy.
• if T’s are different, energy (heat) flows from high T to low T.
• energy flow determined by molecular motions.
THERMOCHEMISTRY (Chapter 6)
– a subset of thermodynamics
– study of the heat given off or absorbed in a chemical reaction.
CHEMICAL REACTIONS AND ENERGY CHANGES
All chemical reactions are accompanied by an ENERGY CHANGE.
Chemical reactions may release heat to the surroundings, e.g.
,
CH4(g) + 2O2(g) → CO2(g) + 2H2O(l) (burning or combustion of natural gas)
If heat is released (given off), the reaction is known as exothermic
.
This arises due to differences in bonding energy of reactants and products.
ALL combustion reactions are exothermic.
If heat is absorbed (taken in), the reaction is endothermic
e.g.
, 6CO2(g) + 6H2O(l) → C6H12O6(s) + 6O2(g) (photosynthesis)
Note: The amount of heat depends on the size of the system.
(This is an EXTENSIVE property, like mass, V and n.)
SIGN CONVENTION FOR HEAT PROCESSES:
PROCESS
SIGN
Heat absorbed BY
the system FROM
the surroundings
(endothermic)
+
NOTES:
3
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