Flashcards in Thermodynamics Deck (26):

1

## Thermodynamics

### The study of heat and its effects

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## Temperature

### A measure of the random kinetic energy of the molecules of a substance

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## How do Fahrenheit, Celsius, and Kelvi relate to one another?

###
Absolute zero: 0 K, -273 degrees Celsius, and -460 degrees Fahrenheit

Freezing Point of Water: 273 K, 0 deg Celsius, and 32 deg Fahrenheit

Boiling Point of Water: 373 K, 100 deg Celsius, and 212 deg Fahrenheit

T(Celsius) = T(Kelvin) - 273

T(Fahrenheit) = 9/5 T(Celsius) + 32

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## Thermal Expansion

###
ΔL = α L ΔT

Where α is a constant that describes how a specific material's length changes as temperature changes

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## Volume Expansion

### ΔV = β V ΔT, where β = 3α

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## Heat

### The energy transferred between two objects as a result of a difference in temperature. Work has to occur in order for heat to transfer from a cooler body to a warmer body.

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## Conduction

### Heat transfers through molecular collisions or direct contact. Metals are the best heat conductors due to their mobile electrons, while gases tend to be poor heat conductors.

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## Convection

### Heat transfers through the physical motion of the heated material, taking place only in liquids and gases. Heated portions rise while cooler portions sink.

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## Radiation

### Heat transfers through electromagnetic radiation.

10

## Why do thermos bottles have a shiny surface on the inside?

### The shiny surface reflects electromagnetic radiation back into the liquid, slowing down heat loss.

11

## Units for heat

### 1 Calorie = 1000 calories = 3.97 Btu = 4184 J

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## Specific Heat

###
Q = mc ΔT = mc(T(final) - T(initial))

Q > 0, heat gain

Q < 0, heat loss

This equation should be used when no phase transition occurs.

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## Heat of Transformation

### The amount of heat required for a phase change, where q = mL

14

## How does temperature change during a phase transition?

### Temperature does not change during a phase transition, remaining constant.

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## Heat of Fusion

### The heat of transformation corresponding to a phase change involving liquids and solids

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## Heat of Vaporization

### The heat of transformation corresponding to a phase change involving liquids and gases

17

## Pressure

###
P = F/ A, where units = Pa = N/ m^2 = kg/ (m s^2)

1 atm = 1.013 X 10^5 Pa

Gas pressure on the container is due to the individual molecular forces the gas exerts on the wall of the container.

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## In problems of thermodynamics, describe the difference between work done BY a gas and work done ON a gas

### Work done BY the system is positive, increasing the volume of the gas, while work done ON the system is negative, decreasing the volume of a gas.

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## Work

###
W = P ΔV

In graphs of P v. V, the total area under the graph is the work done.

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## What is the term for when the pressure remains constant?

### Isobaric

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## First Law of Thermodynamics

### ΔE = Q - W (remember that W done BY system is + and W done ON system is - and heat absorbed is + while heat lost is -)

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## What are some special cases of the First Law of Thermodynamics?

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Adiabatic (Q = 0) ----- ΔU = -W

Constant Volume (W = 0) ----- ΔU = Q

Closed Cycle (ΔU = 0) ----- Q = W

23

## When does internal energy increase (ΔU > 0)?

### When Q > 0, heat absorbed, and W < 0, work done ON system

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## When does internal energy decrease (ΔU < 0)?

### When Q < 0, heat lost, and W > 0, work done BY system

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## Second Law of Thermodynamics

### The entropy of a system combined with the surrounding will either increase (for irreversible processes) or not change (for reversible processes)

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