Thermodynamics equations and definitions

Define an open system:

Define an open system:

A system that can exchange both energy and matter with its surroundings

Define a closed system:

A system that can exchange energy but not matter with its surroundings

Define an isolated system:

A system that can’t exchange matter or energy with tis surroundings

Define a diathermic system:

A system where heat can enter or leave

Define an adiabatic system:

A system where heat can’t enter or leave

Define an isothermal system:

A system that is held at a constant temperature

Define an isobaric system:

A system that is held at a constant pressure

Define an isochoric system:

A system that is held at a constant volume

What is a thermodynamic state function? Give some examples.

A function that describes the state of a system and does NOT depend on how the system came to be. Examples of these include pressure, temperature, volume, mass….. etc

What is a thermodynamic path function? Give some examples.

A means of energy transfer that causes a change in one or more state functions, and DOES depend on how the transfer is performed. There are two path functions, heat (q) and work (w).

What sign (positive or negative) indicates energy leaving / entering the system?

+ve q or w is for energy entering the system

-ve q or w is for energy leaving the system

What is the 0th law of thermodynamics?

When two objects are in thermal equilibrium with a third object, they are in thermal equilibrium with each other.

What is the 1st law of thermodynamics?

Energy can’t be created or destroyed, merely transformed.

What is the 2nd law of thermodynamics?

In a spontaneous process, the entropy of the universe increases.

What is the 3rd law of thermodynamics?

The entropy of a perfect crystal approaches 0 as the absolute temperature approaches 0 K.

What equation goes along with the first law? (its for the change in internal energy)

How would you find the work done by an expanding gas as it pushes against a frictionless piston against a constant external pressure P? How would you use this to find the change in internal energy?

What is the first law equation (change in internal energy) for a gas expansion at zero pressure conditions (eg space)?

What is the first law equation (change in internal energy) for a gas expansion at constant volume conditions (eg at a chemical plant)?

What is the first law equation (change in internal energy) for a gas expansion at a finite pressure in an open vessel (eg in a lab):

What is the equation for a gas expansion at a constant pressure rewritten using the definition of enthalpy?

How would you calculate Won for a reversible expansion? What is the downside to reversible expansions?

Reversible expansions take an infinite amount of time.

What is the expression for the change in entropy under isothermal conditions?

What is the equation for the change in Gibb’s free energy?

delta G needs to be negative for a reaction to be spontaneous

What is the equation for heat capacity C? Why is this limited?

This C value is quite useless as it hasn’t been normalised yet

How do you normalise C by mass? What are the units?

JK-1 Kg-1

How do you normalise C by moles? What are the units?

JK-1 mol-1

What is the expression for the isochoric heat capacity (Cv):

How can you find the isobaric heat capacity using the isochoric heat capacity?

How do you calculate the change in the standard molar heat capacity (in isobaric conditions)?

What is Kirchhoff’s law? What can you do with it?

If you know the change in reaction enthalpy at T1 you can calculate it at T2

How can you calculate the change in entropy for a small temperature change? What does this calculation assume?

It assumes C is the same across the different temperatures

How can you calculate the change in entropy of different phase transitions?

What equation links chemical potential (mu) to the Gibbs energy at constant temperature and pressure?

What is the equation for chemical potential?

a is a thermodynamic activity. In gas phase chemistry it is p / 1 bar, in solution it is c / 1 mol dm-3

What does Delta r G = at equilibrium?

0

What equation links the standard Gibbs free energy of reaction to equilibrium constant K?

What is the Van’t Hoff relation? What are some key assumptions made?

This can be represented as a graph. Positive gradient corresponds to an exothermic reaction and negative is endothermic. The key assumption made is that enthalpy change and entropy change are constant over the temperature range measured.

How can the Van’t Hoff equation be used to predict the temperature dependence of K? What assumption does the equation make?

Assuming that the standard reaction enthalpy is constant over the range Ti → Tf

How do you derive the equation for the reversible expansion of an ideal gas in isothermal conditions?