This presentation is the property of its rightful owner.
1 / 40

# Thermodynamics – study of energy First law of thermodynamics Energy of the universe is constant PowerPoint PPT Presentation

Thermodynamics – study of energy First law of thermodynamics Energy of the universe is constant Energy can not be created or destroyed. Energy is the ability to do work or produce heat. 2 types of Energy. Kinetic energy Energy of motion E = ½ mv 2. Potential energy

Thermodynamics – study of energy First law of thermodynamics Energy of the universe is constant

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

#### Presentation Transcript

• Thermodynamics – study of energy

• First law of thermodynamics

• Energy of the universe is constant

• Energy can not be created or destroyed

• Energy is the ability to do work or produce heat.

• 2 types of Energy

Kinetic energy

Energy of motion

E = ½ mv2

Potential energy

Energy of position

• Law of conservation of energy

• Energy can not be created or destroyed but can be converted from one form to another

• Ex chemical energy (gas) can be converted to mechanical and thermal energy

• Internal energy = E

“sum” of kinetic & potential energies of all “particles” in a system

Internal energy can be transferred by two types of energy flow:

• Heat (q) (q = quantity of heat)

• Work (w)

E = q + w

Change of energy in a

system

### Measuring Energy Changes

• common energy units for heat are the calorie and the joule.

• Calorie – the amount of energy (heat) required to raise the temperature of one gram of water 1oC.

• Joule – heat required to raise the temperature of 1 g of water by 0.24 K

1 calorie = 4.184 joules

• System – part of the universe on which we focus attention

• Surroundings – everything else in the universe

• Ex. Burning a match is the system releases heat to surroundings

Endothermic – energy flows into system

Exothermic – energy flows out of system

• C- Specific heat capacity energy required to change the mass of one gram of a substance by one degree Celsius. [joule/gram °C]

• Like energy storage bank

• C- Specific heat capacity energy required to change the mass of one gram of a substance by one degree Celsius. [joule/gram °C]

• Like energy storage bank

• Water has a high specific heat capacity that means it takes a lot of heat (joules) to increase the temperature of water compared to metals (water better at storing energy than metals

### B. Measuring Energy Changes

• To calculate the energy required for a reaction:

Q = C  m t

Q = C  m t

How much heat is required to warm 145 g of water from 25 *C to 65 *C

Q = m x C t

How much heat is required to warm 145 g of water from 25 *C to 65 *C the specific heat of liquid water is 4.184 J/g *C

Q = m x C t

Q = 145 g x 4.184 J x (65 *C - 25 *C)

g *C

Q = m x C t

How much heat is required to warm 145 g of water from 25 *C to 65 *C the specific heat of liquid water is 4.184 J/g *C

Q = C  m t

Q = 145 g x 4.184 J x (65 *C - 25 *C)

g *C

Q = 145 x 4.184 J x 40

Q = 24,267 joules

A quantity of water is heated from 20.0 *C to 48.3 *C by absorbing 623 Joules of heat energy, what is the mass of the water? Specific heat of water is 4.184 J/g *C

Q = C  m t

__Q__ = m

C x t

A quantity of water is heated from 20.0 *C to 48.3 *C by absorbing 623 Joules of heat energy, what is the mass of the water? Specific heat of water is 4.184 J/g *C

Q = C  m t

__Q__ = m

C x t

623 J = m

4.184 J /g *C x (48.3 *C - 20 *C)

A quantity of water is heated from 20.0 *C to 48.3 *C by absorbing 623 Joules of heat energy, what is the mass of the water? Specific heat of water is 4.184 J/g *C

Q = C  m t

__Q__ = m

C x t

623 J = m

4.184 J /g *C x (48.3 *C - 20 *C)

623 J = m

4.184 J /g *C x (28.3 *C)

5.26 g = m

In a household radiator a 25.5 g of steam at 100 *C condenses (changes from gas to liquid) How much heat is released? Heat of vaporization is 2260 J/g

Q = m Hvap

In a household radiator a 25.5 g of steam at 100 *C condenses (changes from gas to liquid) How much heat is released? Heat of vaporization is 2260 J/g

Q = m Hvap

Q = 25.5 g x 2260 J/g

Q = 57,630 J

Objectives

• To consider the heat (enthalpy) of chemical reactions

• To understand Hess’s Law

### A. Thermochemistry (Enthalpy)

• Enthalpy, H– energy function

• At constant pressure H is equal to the energy that flows as heat.

Hp = heat = q

ΔH = q  (valid for constant pressure ONLY!)

### A. Thermochemistry

Calorimetry

• Enthalpy, H is measured using a calorimeter.

### B. Hess’s Law

• For a particular reaction, the change in enthalpy is the same whether the reaction takes place in one step or a series of steps.

• Example:

N2(g) + 2O2(g) 2NO2(g)H1 = 68 kJ

Objectives

• To understand how the quality of energy changes as it is used

• To consider the energy resources of our world

• To understand energy as a driving force for natural processes

### A. Quality Versus Quantity of Energy

• When we use energy to do work we degrade its usefulness.

### A. Quality Versus Quantity of Energy

• Petroleum as energy

### B. Energy and Our World

• Fossil fuel – carbon based molecules from decomposing plants and animals

• Energy source for United States

### B. Energy and Our World

• Petroleum – thick liquids composed of mainly hydrocarbons

• Hydrocarbon – compound composed of C and H

### B. Energy and Our World

• Natural gas – gas composed of hydrocarbons

### B. Energy and Our World

• Coal – formed from the remains of plants under high pressure and heat over time

### B. Energy and Our World

• Effects of carbon dioxide on climate

• Greenhouse effect

### B. Energy and Our World

• Effects of carbon dioxide on climate

• Atmospheric CO2

• Controlled by water cycle

• Could increase temperature by 10oC

### B. Energy and Our World

• New energy sources

• Solar

• Nuclear

• Biomass

• Wind

• Synthetic fuels

### C. Energy as a Driving Force

• Natural processes occur in the direction that leads to an increase in the disorder of the universe.

• Example:

• Consider a gas trapped as shown

### C. Energy as a Driving Force

• What happens when the valve is opened?

### C. Energy as a Driving Force

• Two driving forces

### C. Energy as a Driving Force

• In a given process concentrated energy is dispersed widely.

• This happens in every exothermic process.

### C. Energy as a Driving Force

• Molecules of a substance spread out to occupy a larger volume.

• Processes are favored if they involve energy and matter spread.

### C. Energy as a Driving Force

• Entropy, S – function which keeps track of the tendency for the components of the universe to become disordered

### C. Energy as a Driving Force

• What happens to the disorder in the universe as energy and matter spread?

### C. Energy as a Driving Force

• Second law of thermodynamics

• The entropy of the universe is always increasing.