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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

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

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Thermodynamics study of energy first law of thermodynamics energy of the universe is constant

  • Thermodynamics – study of energy

  • First law of thermodynamics

    • Energy of the universe is constant

    • Energy can not be created or destroyed


Thermodynamics study of energy first law of thermodynamics energy of the universe is constant

  • 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


Thermodynamics study of energy first law of thermodynamics energy of the universe is constant

  • 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


Thermodynamics study of energy first law of thermodynamics energy of the universe is constant

  • 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

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


Thermodynamics study of energy first law of thermodynamics energy of the universe is constant

  • 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


Thermodynamics study of energy first law of thermodynamics energy of the universe is constant

Endothermic – energy flows into system

Exothermic – energy flows out of system


Thermodynamics study of energy first law of thermodynamics energy of the universe is constant

  • 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


Thermodynamics study of energy first law of thermodynamics energy of the universe is constant

  • 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

B. Measuring Energy Changes

  • To calculate the energy required for a reaction:

Q = C  m t


Thermodynamics study of energy first law of thermodynamics energy of the universe is constant

Q = C  m t

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


Thermodynamics study of energy first law of thermodynamics energy of the universe is constant

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


Thermodynamics study of energy first law of thermodynamics energy of the universe is constant

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


Thermodynamics study of energy first law of thermodynamics energy of the universe is constant

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


Thermodynamics study of energy first law of thermodynamics energy of the universe is constant

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)


Thermodynamics study of energy first law of thermodynamics energy of the universe is constant

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


Thermodynamics study of energy first law of thermodynamics energy of the universe is constant

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


Thermodynamics study of energy first law of thermodynamics energy of the universe is constant

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


Thermodynamics study of energy first law of thermodynamics energy of the universe is constant

Objectives

  • To consider the heat (enthalpy) of chemical reactions

  • To understand Hess’s Law


A thermochemistry enthalpy

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

A. Thermochemistry

Calorimetry

  • Enthalpy, H is measured using a calorimeter.


B hess s law

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


Thermodynamics study of energy first law of thermodynamics energy of the universe is constant

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

A. Quality Versus Quantity of Energy

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


A quality versus quantity of energy1

A. Quality Versus Quantity of Energy

  • Petroleum as energy


B energy and our world

B. Energy and Our World

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

    • Energy source for United States


B energy and our world1

B. Energy and Our World

  • Petroleum – thick liquids composed of mainly hydrocarbons

  • Hydrocarbon – compound composed of C and H


B energy and our world2

B. Energy and Our World

  • Natural gas – gas composed of hydrocarbons


B energy and our world3

B. Energy and Our World

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


B energy and our world4

B. Energy and Our World

  • Effects of carbon dioxide on climate

  • Greenhouse effect


B energy and our world5

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 world6

B. Energy and Our World

  • New energy sources

  • Solar

  • Nuclear

  • Biomass

  • Wind

  • Synthetic fuels


C energy as a driving force

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 force1

C. Energy as a Driving Force

  • What happens when the valve is opened?


C energy as a driving force2

C. Energy as a Driving Force

  • Two driving forces

  • Energy spread

  • Matter spread


C energy as a driving force3

C. Energy as a Driving Force

  • Energy spread

  • In a given process concentrated energy is dispersed widely.

  • This happens in every exothermic process.


C energy as a driving force4

C. Energy as a Driving Force

  • Matter spread

  • 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 force5

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 force6

C. Energy as a Driving Force

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


C energy as a driving force7

C. Energy as a Driving Force

  • Second law of thermodynamics

  • The entropy of the universe is always increasing.


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