Physical Chemistry: Reactivity Flashcards
What is thermodynamics?
The study of the way different types of energy interconvert.
What is the system?
The part of the world being studied.
What are the surroundings?
The rest of the world outside of the system.
What can be measured about a system?
The energy change of a system.
The energy of a system cannot be measured.
What is an open system?
A system where both matter and energy can be exchanged with the surroundings.
For example, a reaction taking place in a beaker.
What is a closed system?
A system that contains a fixed amount of matter but energy can be exchanged.
For example, a sealed reaction vessel.
What is an isolated system?
A system where there can be no exchange of energy or matter with the surroundings.
For example, a sealed, insulated vacuum flask.
What is energy?
The capacity to do work.
How is work done?
When moving against a force.
What is the equation for work done?
w = Fs
w = Work Done (J)
F = Force (N)
s = Distance (m)
What is the internal energy?
The total capacity for a system to do work.
It is denoted by the symbol, U.
What is the intermolecular potential energy in an ideal gas?
Zero.
This is because there are no forces between the molecules.
What does the internal energy of an ideal gas depend on?
Temperature, as the internal energy is purely kinetic.
What is the internal energy of an ideal gas independent of?
The volume.
What is the first law of thermodynamics?
Energy can neither be created nor destroyed, it can only be transformed from one form into another.
If work is done by a system, what happens to its internal energy?
It decreases.
If work is done on a system, what happens to its internal energy?
It increases.
What is heat?
Energy that flows from high-temperature objects to low-temperature objects.
What is thermal equilibrium?
Where there is no heat flow between two objects as they are the same temperature.
This is sometimes called the 0th law of thermodynamics.
What is the molar heat capacity equation?
q = nCΔT
q = amount of heat supplied (J)
n = amount of substance (mol)
C = molar heat capacity (J mol⁻¹ K⁻¹)
ΔT = change in temperature (K)
How can the molar heat capacity be measured in gases?
It can be measured in two ways: at a constant pressure (Cₚ) or constant volume (Cᵥ).
What is the heat capacity of a substance related to?
The number of degrees of freedom possessed by its molecules.
What are the two types of work?
Expansion work.
Non expansion work.
What is expansion work?
Involves a change in the volume of the system.
For example, the work done by a reaction with gaseous products.
What is non-expansion work?
Does not involve a change in volume of the system.
For example, the electrical work done by a battery.
What is the irreversible constant pressure expansion equation?
W = pₑₓΔV
W = work done (J)
pₑₓ = external pressure
ΔV = change in volume
What corresponds to the area under a Boyle’s Law curve?
The work done for an ideal gas expanding reversibly at a constant temperature.
What is a statement of the second law of thermodynamics?
A process must occur reversibly to do the maximum possible work.
What is the equation of internal energy when work and heat are taken into account?
ΔU = q + w
ΔU = change in internal energy
q = heat (it is positive if heat is supplied to the system and negative if heat is released by the system)
w = work (positive if work is done on the system, negative if work is done by the system).
In an ideal gas, if the temperature is kept constant, what happens the internal energy.
It remains constant too.
What are the consequences of the first law of thermodynamics?
Energy is conserved - heat and work are equivalent forms of energy.
For a system at constant volume, there is no expansion work.
Internal energy is a state function.
What are state functions?
Quantities such as pressure, volume, temperature which depend only on the state of the system.
If the system is changed from one state to another, the change in a state function is independent of how the change was brought about.
What are path functions?
Quantities like work and heat which depend on the path between the states.
Path functions depend on how the change was brought about.
What is an intensive property?
A property that does not depend on the quantity of the substance present.
What is an extensive property?
A property that depends on the quantity of the substance present.
What is enthalpy?
The heat change at a constant pressure.
What is enthalpy defined as?
H = U + pV
What is the change in enthalpy equal to?
ΔH = ΔU + pΔV
= q + w + pΔV
= q - pΔV + pΔV
= qₚ
What is the heat transferred at a constant pressure (qₚ) equal to?
qₚ = nCₚΔT
What is an exothermic process?
ΔH < 0, so heat is released from the system at constant pressure.
What is an endothermic process?
ΔH > 0, so that heat is absorbed by the system at constant pressure.
What is the standard molar enthalpy of melting?
The enthalpy change which occurs when 1 mol of a pure solid melts to form a liquid at its melting point and 1 bar pressure.
What is the standard molar enthalpy of vapourisation?
The enthalpy change which occurs when 1 mol of a pure liquid boils to form a gas at its boiling point and 1 bar pressure.
What is Hess’s Law?
The overall reaction enthalpy is the sum of the reaction enthalpies of the steps into which the reaction can be divided.
What type of function is enthalpy?
A state function.
This allows Hess’s law to be true, as its value is independent of the path chosen.
What is the standard enthalpy of formation?
The standard reaction enthalpy for the formation of a compound in its standard state from elements in their standard state.
What is the standard enthalpy of for an element in its standard state?
Zero.
How is the enthalpy change for a reaction calculated?
The sum of the enthalpy of the products - the sum of the enthalpy of the reactants.
What is electrochemistry?
The study of chemical reactions that take place at the surface of an electrode.
What is an electrode?
An electronic conductor which is immersed in an electrolyte.
What is an electrolyte?
An ionic conductor that is usually an ionic solution.
What reactions occur at electrodes?
Redox reactions.
What is an electrochemical cell?
Two electrodes in contact with an electrolyte.
What is a galvanic cell?
A cell that produces electricity when a spontaneous reaction takes place within the cell.
What reaction occurs at the anode?
Oxidation.
What reaction occurs at the cathode?
Reduction.
What is an electrolytic cell?
A cell where a non-spontaneous reaction is driven by an external current.
What is a salt bridge?
A tube which contains a concentrated salt solution. It allows ions to flow between the electrolytes.
How many degrees of freedom does a molecule have?
3 times the number of atoms.
How many vibrational modes does a linear molecule have?
3N - 5.
(Where N is the number of atoms)
How many vibrational modes does a non-linear molecule have?
3N - 6.
(Where N is the number of atoms)
