A CRASH COURSE IN THERMODYNAMICS

Darynn Magee

WHAT IS THERMODYNAMICS?

The science of heat or energy flow in chemical reactions. The study of the transformation of energy into different forms

A BRIEF HISTORY:

Otto Von Guericke (1650): Designed the world’s first vacuum pump. Known as the Magdeburg

Hemispheres, the hemispheres were held together with a force of over 20,000N or 4,500.lbs

A BRIEF HISTORY:

Robert Boyle and Robert Hooke (1656): Built the first air pump. During their studies, Boyle and hook noticed a

correlation between temperature, pressure and volume. Developed Boyle’s Law

A BRIEF HISTORY Sadi Carnot (1824): Known as “the father of

thermodynamics” Published Reflections on the Motive Power of

Fire.

A BRIEF HISTORY:

James Joule (1849): coined the term “thermodynamics” as the science of the relation between heat and power

THE THERMODYNAMICIST’S VIEW OF THE UNIVERSE:

The universe is defined as:Universe = System + Surroundings

TYPES OF SYSTEMS:

Open: Both mass and energy is exchanged between the system and its

surroundings

Closed: Energy is exchanged between the system and its surroundings but mass is conserved

Isolated: No exchange of mass or energy between the system and its surroundings.

OPEN SYSTEMS

CLOSED SYSTEMS

ISOLATED SYSTEMS

ENERGY FLOW WITHIN A SYSTEM

Exothermic Reactions: Energy flows from the system into its

surroundings. The internal energy of the system goes down.

ENERGY FLOW WITHIN A SYSTEM

Endothermic reactions: Energy flows from the surroundings to the

system. Internal energy of the system goes up.

LAWS OF THERMODYNAMICS

1st law: The Law of Conservation of energy

Energy cannot be created or destroyed. It can only change forms.

The increase in the internal energy of a system is equal to the amount of energy added by heating the system, minus the amount lost as a result of the work done by the system on its surroundings.

•U=q-pΔV

LAWS OF THERMODYNAMICS

1st Law (continued): U=q-pΔV

U= internal energy in joules (J) q= heat flow in joules (J) P= pressure in atmospheres (atm) ΔV= Change in volume (V2-V1) in liters (L)

LAWS OF THERMODYNAMICS

1st law sample problem:

A balloon with a volume of 1L and a pressure of 1 atm sits in the Sun for one hour. The Sun applies 100J of heat to the balloon and its volume increases to 1.25L. What is the internal energy of the balloon?

LAWS OF THERMODYNAMICS

Answer: 99.75J

U=q-pΔVU=100-1(1.25-1)U=99.75J

LAWS OF THERMODYNAMICS

2nd Law: The entropy (disorder) of the universe is always increasing, for spontaneous reactions.

Entropy is used to quantify the extent of disorder resulting from the dispersal of energy and matter

Units of J/mol×K

LAWS OF THERMODYNAMICS

2nd law (continued): Disorder is more probable than order, so it

stands that an ordered system will become disordered over time.

LAWS OF THERMODYNAMICS

2nd law (continued): The entropy of the universe increases naturally.

Reducing the entropy of a system takes work. The entropy of the universe never goes down regardless of how much work we put into it.

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LAWS OF THERMODYNAMICS

2nd law (continued): The 2nd law allows us to predict the equilibrium

conditions of a given chemical process as well as the direction of spontaneous change towards equilibrium.

If we took given amounts of reactants and products of a chemical reaction and mix them together, the 2nd law would help us figure out how much of the reactants and products will be left over after the they are mixed.

LAWS OF THERMODYNAMICS

3rd law: As a system approaches absolute zero (0K), all processes cease and the entropy of the system approaches a minimum value.

The most ordered state is a crystalline structure at 0K. There is no entropy (disorder)

in a crystalline structure at 0K. Entropy = 0.

Other physical states at 0K can have residual entropy.

LAWS OF THERMODYNAMICS

3rd law (continued): The entropy of a substance is the amount of

entropy gained in order to convert it from a crystalline structure at 0K to its current form.

In general, in terms of entropy:

Solid < liquid < gas

WRAP UP

What are the characteristics of open, closed, and isolated systems? Give some examples of each

What are endothermic and exothermic reactions?

How does the system do work on its surroundings when the heat is applied? (1st law)

What is entropy? (2nd law) What would the world be like if there was no

entropy? (3rd law)