386 Thermodynamics Flashcards
Definition of Thermodynamics
study of inter-conversion of heat and other forms of energy
definition of spontaneous reaction
physical or chemical change that occurs by itself
definition of non-spontaneous reaction
phyisical or change that does NOT occur by itself
Type of Thermodynamic Systems
Open
Closed
Isolated
What is an open thermodynamic system
system that can exchange both mass and energy with the surroundings
what is a closed system
system that can exchange heat but not mass with the surroundings
What is an isolated system?
a system where there is no exchange or either mass or heat with the surroundings
What’s the goal of the Laws of Thermodynamics?
Predict the behavious of physical and chemical systems
The First Law of Thermodynamics is also known as what?
Law of Conservation of Energy
What is the First Law of Conservation of Energy?
The total energy of the universe is constant.
Energy can neither be created nor destroyed
What is the Heat of Reaction?
quantity of heat required to return a system to its original temperation, after completion of the chemical reaction. There is a gain or loss of heat to do so.
What is an exothermic reaction?
chemical reqction where heat is released from the system
quantity of heat (q) is NEGATIVE
What is an endothermic reaction?
reaction where heat must be added to the system to return it to its original temperature.
quantity of heat(q) is positive
How are thermodynamic quantities indicated ?
by magnitude of change (by a number)
by direction of the flow ( + or -)
What are State Functions?
property of a system that depends on its present state (Temp and Pressure) and is independent of the previous history of the system.
TEMPERATURE is key
Give examples of State Functions?
Enthalpy
Define enthalpy
amount of energy within a substance that can be converted to heat Delta Hrxn = Sum Delta Hprod - Sum Delta Hreac Enthalpy change depends on state of reactant and products The states (gas,liquids, solid or aqueous)
define atom and molecule
single unit of an element
define mole
number of molecules in a standard amount of an element
1 mole = 32 g oxygen
what is avogadro’s number ?
number of molecules in 1 mole of oxygen
what is atomic weight?
weight in grams of avogadro’s number of molecules in 1 type of atom
oxygen = 16g
what is molecular weight?
weight in grams of avogadro’s number of molecules in one mole of a compound
eg HCl = 1.01g + 35.5g = 36.5g
What is Thermodynamic standard state of a substance?
standard conditions
Pressure = 1 atm
Temperature = 25C
How is standard state indicated?
Delta Hrxn with superscript 0
What does constant T and P mean?
Constant temp and pressure means initial and final conditions are the same
What does standard enthalpy change mean?
Delta H rxn superscript 0
when a specified number of moles of reactants, all STP are converted completely to the specified number of moles of products
delta H ==== change in enthalpy
0 = STP
rxn = entire reaction process
What is standated molar enthalpy of formation ?
Delta Hf superscript 0
Enthalpy change for a reqction in which 1 mole of substance in a specified state is formed from its elements in their standard states.
Value is 0 for any element in its standard state
Does magnitude of Delta H depend on amount of reactants ?
Yes. double reactants, doube enthalpy
What happens if you reverse a chemical reaction?
results in same magnitude of enthalpy (deltaH) but opposite sign
Define Hess’s Law
Heat of Reaction - Hess’ Law
enthalpy change for any reaction depends on products and reactants.
independent of the pathway or steps.
Delta Hrxn superscript 0 = Delta H a superscript 0 + Delta H b superscript…
Bond Energies
amount of energy required to break and form one mole of bonds in a covalent substance in the gaseous state at Temp and Pressure
Triple bond > double bond > single bond
What is the formula to use bond energies to estimate heat of reactions
FOR GAS ONLY
Delta H rxn superscript 0 =
Sum Bond Energy react - Sum Bond Energy prod
What are the 2 cases of spontaneity of Physical and Chemical Changes
Spontaneous (product favoured)
Non-Spontaneous (reactant favoured)
Define Spontaneous Physical and Chemical Changes
change for which the collection of products are thermodynamically MORE stable than the collection of reactants under the given conditions
Define Non-Spontaneous Physical and Chemical Changes
change for which the collection of products are thermodynamically LESS stable than the collection of reactants under the given conditions
Reaction is VERY slow
Reactants are themodynamically MORE stable than the products
What are the possible outcomes when it comes to spontaneous and non-spontaneous physical and chemical reactions ?
changes that are SPONTANEOUS under ALL conditions
changes that are NON-SPONTANEOUS under ALL conditions
most changes are spontaneous under SOME conditions
What else needs to be involved in addition to enthalpy for a the direction of a spontaneous change?
disorder
less random»_space;»> more random OR
more order»_space;»> less order
Name the types of States Functions
Enthalpy
Entropy
What’s the Second Law of Thermodynamics
Total entropy of a system and its surroundings always increases in a spontaneous process.
Delta S system + Delta S surrounding > 0
aka rxn + system > 0
What’s the Third Law of Thermodynamics
Entropy of all pure crystalline materials at absolute zero (0K) is 0 Kelvin
What happens at absolute zero according to the Laws of Thermodynamics ?
no molecular motion –> no motion –> S = 04Entropy has a defined starting point
Delta S superscript 0
entropy change of any substance at any condition such as 298 K
S298 superscript 0 is ALWAYS + for compounds and elements
Delta Srxn superscript 0 =
Sum n Sprod superscript 0 = Sum n Sreac superscript 0
where n = moles
What are the processes that increase entropy?
inc disorder
phase changes inc disorder (melting, vapourization) dec disorder (freezing, condensation)` temp changes (inc T, inc random motion) volume changes (inc V inc random motion) mixing of substances H gas instead of water = mix of elements and inc disorder inc number of particles H20 vs. H202 -- inc particles changes in no. moles of gaseos substances
What is free energy ?
energy is the capacity to do work
is DELTA S is NEGATIVE, Heat can be used to inc disorder in the system
What is Gibbs Free Energy ?
indicates spontaneity of a reaction or physical change at constant T and P
Dela G = Delta H - T Delta S (at constant T and P)
What is the relationship between Delta G and Spontaneity at constant T and P
Delta G is +ve —– rxn non-spontaneous and react favoured
Delta G is 0 —–reaction is at equilibrium
Delta G is -ve —– rxn is spontaneous (prod favoured)
What is the relationship between Enthalpy, Entropy and Free Energy ?
G = H - TS
G— Free Energy
H — Enthalpy
S — Entropy
When can Delta G be negative ?
when Delta H is negative (exothermic rxn – heat released)
When delta S is positive (greater disorder)
What are the Delta G values?
Delta G superscript 0 – standard state of free energy
1 atm, 25 C, 298K)
Delta Gf superscript 0 = standard molar free energy of formation for elements in their standard state = 0
