Thermochemistry Flashcards
What is Thermochemistry?
Thermochemistry is the study of heat changes that accompany chemical reaction and physical
changes.
What is an Endothermic Reaction
A reaction that is accompanied by absorption of heat from the surroundings which results in the decrease of surrounding temperature.
know how to draw and label exothermic graph
Example of Endothermic Reaction
-Melting of ice
-Decomposition of limestone by heating
-Photosynthesis
-Dissolving certain ammonium salts in water
What is an Exothermic Reaction?
A Reaction involves the evolution of heat to the surroundings increasing surrounding temperature
know how to draw adnd label exothermic graph
Examples of Exothermic Reaction
-Combustion of fuels
-Oxidation of carbohydrates in bodies of plants and animals
-Reaction of water with quicklime
What is Enthalpy
The heat content of a system
What is Enthalpy Change/Heat of Reaction(∆H)
The energy exchange between a
chemical reaction and surroundings at constant pressure
What is Enthalpy change mathematically
∆H = ∑Hproducts - ∑Hreactants
-Exothermic reaction the ∆H is negative
-Endothermic reaction ∆H is positive
NOTE
- The enthalpy of elements in their standard state is zero
- Enthalpy of a compound is equal to the molar enthalpy of formation of the compound
Know how to balance thermochemical equations
What is the Standard Enthalpy of a Reaction?
The standard state of solid or liquid is the pure substance at pressure of 1atm (1bar) and temperature of 298K (25℃).
What are enthalpy changes during phase transition?
The heat absorbed during the processes of vaporization, melting, solidification and other physical changes which occur without change in temp and pressure.
What standard enthalpy of fusion
The quantity of heat absorbed when 1 mole of crystalline solid is melted at constant temperature and pressure
What is standard enthalpy of sublimation
The quantity of heat required to sublime one mole of solid at standard temp and pressure
What is standard enthalpy of formation?
The quantity of heated liberated or absorbed when 1 mole of a compound is formed from its elements in their standard states.
What is standard enthalpy of solution?
The enthalpy change when on mole of a substance dissolves to produce and infinitely dilute solution under standard condition.
What is standard enthalpy change of atomization?
The enthalpy change when one mole of gaseous atom is formed from its element under standard conditions
What is Bond Energy
The amount of energy needed to break a specific covalent bond..
∆H reaction = bonds broken – bond formed
What is Specific Heat Capacity
Specific heat capacity (c ) is the quantity of heat required to raise the temperature of 1 gram of a substance by 1℃
C= q/m∆T
What is the standard enthalpy of vaporization?
The quantity of heat required to vaporize 1 mole of liquid at its boiling point and constant pressure
What is the standard enthalpy of solidification?
The enthalpy change when one mole of a substance transform from liquid to solid under standard condition
What is standard enthalpy change of hydration?
The enthalpy change
when one mole of the hydrated salt is formed from one of the anhydrous salt under
standard condition
State Hess’s Law
The law that states that the total enthalpy change in a chemical reaction is independent of the route by which the chemical reaction takes place as long as the initial and final conditions are the
same
Know the diagram for hess’s law
What is standard enthalpy of condensation?
The enthalpy change when one mole of substance transform gas to liquid under standard condition.
What is standard enthalpy of neutralization
The enthalpy change when one mole of water is formed by the reaction of acid with a base under standard condition
What is standard enthalpy of combustion?
The enthalpy change when one mold of a substances burned completely under standard conditions.
What is Heat Capacity(C)?
The amount of heat required to raise the temperature of an object by 1k or 1℃
C= q/∆T , unit is J/℃
What is Specific Heat Capacity(c)?
Specific heat capacity (c ) is the quantity of heat required to raise the temperature of 1 gram of a substance by 1℃
C= q/m∆T
What are the First Law of Thermodynamics
-Energy is conserved; it can neither be created or destroyed
What are the limitations of the First Law of Thermodynamics?
The first law by itself tells nothing about the direction of a spontaneous change
What are the Second Law of Thermodynamics
In an isolated system, natural processes are spontaneous when they lead to an increase in disorder, or entropy
What are the Third Law of Thermodynamics
The entropy of a perfect crystal is zero when the temperature of the crystal is equal to absolute zero (0K)
What is an Open System
A system in which there is an exchange of energy and matter between the system and surrounding
What is a Closed System?
A system in which no exchange in matter, but exchange of energy is possible between system and surroundings.
What is a Isolated System?
A system in which there is no exchange in of energy or matter between the system and surroundings
What is a Thermodynamic Process?
It is defined as the pathway of series of intermediate changes that occur when a system is changed from its initial to its final state
What is an Adiabatic Process?
A process in which there is no exchange in heat with the surroundings
What is a Isobaric Process
A process in which pressure of the system remain constant
What is an Isochoric Process?
A process in which the volume of the system remains the same
What is a Cyclic Process
The process which brings back the system to its initial state
What are Spontaneous process?
They are processes that occur on their own accord when the transformation of the system from initial to final state is favorable in one direction.
What are non-spontaneous process?
These are processes that do not occur on their own accord they can occur by supplying energy from outside of the system
What is a Reversible Process
This is a process where the series of changes carried out on the system during its transformation can be reversed.
What is and Irreversible Procces?
A process which cannot be retraced to its initial state without making a permanent change in the surroundings.
What are Thermodynamic Properties?
Measurable properties that define a system completely. They can be intensive or extensive.
What are Intensive properties?
Those that are independent of the size(mass. of the system such as temperature, pressure and density.
What are Extensive Properties
Those that are dependent on size or amount of substance in the system, such as mass, volume, internal energy, free energy, enthalpy, entropy
What is Heat (q)
This refers to the disordered flow of energy between system and surroundings when there is temperature difference
What is Work (w)
The ordered flow of energy between the system and surroundings when
there is no temperature difference
What is Internal Energy (U)
This is the sum of all the possible forms of energy in a system
Properties of Change in internal energy (∆U):
-∆U is POSITIVE when the system gains energy
-∆U is NEGATIVE when the system loses energy
(+)heat is absorbed or work is done ON the system
(-)heat is lost and/or work is done BY the system
What is Entropy
The number of possible arrangements of the particles and energy of a given system or the measure of how disordered a system is
How does can you predict S° when temperature is changing?
For a given substance, entropy increases as the temperature
increases
The kinetc energies of gas partcles in
a sample are distributed over a range, which becomes wider as the temperature rises
How does can you predict S° when there is a change in physical states and phase?
For a phase change such as melting or vaporizing, heat is absorbed (q > 0).. The particles have more freedom of motion, and their energy is more dispersed, so the entropy change is positive.
How does can you predict S° when dissolving a solid to a liquid?
The entropy generally increases when a solid is dissolved in a
solvent
There are exceptions like when AlCl3
dissolves in water, even though entropy of Cl-
(aq). is positve, the overall entropy of aqueous
AlCl3 is lower than that of solid AlCl3
How does can you predict S° when dissolving a gas?
The entropy of a solution of a gas in a liquid or a solid is always less than the entropy
of the gas
Gases already have so much freedom of moton and such
highly dispersed energy that they always lose freedom when they dissolve in a liquid or solid.
How does can you predict S° when dealing with changes in atomic size
Simpler substances with fewer atoms have lower entropy values than the complex substances with more atoms.
Harder substances have lower entropy than sofer substances of the same
type/ allotrope. e.g diamond has a smaller entropy than graphite.
What is Standard Entropy of Reaction (∆Srxn)
The entropy change that occurs when all reactants and products are in their standard
states
∆S○rxn=∑ S○products − ∑S○reactants
What is Gibbs Free Energy (G)?
The measure of the spontaneity of a process
Josiah Willard Gibbs (1839-1903.)
know how to derive gibbs free energy
What does the sign of G mean
(+G)Nonspontaneous
(-G)Spontaneous
When is a reaction is spontaneous at all temperatures?
∆H -
∆S +
∆H is negatve and ∆S is positve, so -T∆S is negatve; thus, ∆G is always negatve.
When is a reaction is nonspontaneous at all temperatures?
∆H +
∆S -
∆H is positve and ∆S is negatve, so -T∆S is positve; thus, ∆G is always positve.
When is reaction is spontaneous at higher temperatures
∆H+
∆S +
When is reaction is spontaneous at lower temperatures
: ∆H -
∆S -
