Lecture Thirteen Flashcards Preview

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1
Q

Define temperature and heat.

A

Temperature is the scale which may be used to indicate degrees of hot and cold. That is, when two objects are at different temperatures are able to transfer heat, heat will flow from the hotter to the cooler body.

Heat is the energy that transfers from a hotter to a cooler object in this process.

2
Q

Define open, closed and isolated systems.

A

Open systems - can gain or lose MASS and ENERGY across this boundaries. E.g. the human body.

Closed systems - can absorb or release ENERGY, but NOT MASS, across the boundary. The mass of a closed system is constant, no matter what happens inside. E.g. a light bulb.

Isolated system - CANNOT EXCHANGE MATTER OR ENERGY with their surroundings. Because energy cannot be created or destroyed, the energy of an isolate system is constant, no matter what happens inside. A stoppered vacuum flask is a good approximation of an isolated system. Processes that occur within an isolated system with no heat transfer to the surroundings are called adiabatic.

3
Q

What is a joule?

A

The SI unit of energy, work (motion against an opposing force) and heat is the joule (J).
A joule is the amount of kinetic energy possessed by a 2 kg object moving at a speed of one meter per second.

4
Q

What are the symbols and meanings of internal energy, enthalpy, entropy and gibbs energy?

A

Internal energy:
U.
Is the sum of all the nuclear, electric, vibrational, rotational, translational and interaction energies of all the individual particles in a sample of matter.
The total energy in a system.
In a perfectly isolated system: the change in U = 0.
I.e. energy can change form by cannot be created not destroyed.

Enthalpy:
H.
Is a unction relate to the heat absorbed or evolved by a chemical system and may be determines by measuring the temperature change that occurs during a chemical reaction or physical change under conditions of constant pressure.

Entropy:
S.
Is a measure of the number of ways energy is distributed throughout a chemical system. Its value is related to the enthalpy of the system at a particular temperature.
Can be defined as the level of disorder in a system.

Gibbs energy:
G.
Is defined as G = H - T*S.

5
Q

Define exothermic and endothermic reactions.

A

Exothermic: A release of energy from the system into the surroundings.
Denoted by a negative change in enthalpy and Gibbs free energy.

Endothermic: An absorption of energy from the surroundings into the system.
Denoted by a positive change in enthalpy and Gibbs free energy.

6
Q

What is a state function?

A

Pressure, temperature, volume and internal energy are all state functions.
State functions have unique values once the state of the system is defines.
This means that the change in internal energy depends only on the initial and final states of the system ad s independent of the path connecting these states.

7
Q

What is a path function?

A

Functions like heat (q) and work (w) have no meaning in an equilibrium state, and are observed only as consequences of a particular process of change.
The separate values of heat (q) and work (w) are not predictable from the change in internal energy (only their sum). They depend on the way the change occurs and this are path functions.

8
Q

What is the first law of thermodynamics?

A

Based on three simple ideas that arise from observations:

1) Energy is conserved.
If energy is conserved this means that is cannot be created or destroyed.
Therefore any change in the internal energy of a system must be the result of work done or heat change in a system.
Energy given out by a system = energy gained by surroundings.

2) Heat and work can produce equivalent effects.
3) The only ways that energy can be transferred is though heat or work.