Section 10.4

Using Energy in the Real World

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

2. To understand energy as the driving force for natural processes

3. To consider the energy resources of our world

Objectives

Big Bang

Section 10.4

Using Energy in the Real World

• Energy is neither created nor destroyed…but…..• When we use energy to do work or provide heat we

degrade its usefulness

A. The Direction of Energy Flow

Which is more likely to happen – a hot cup of coffee cools to room temperature or a cold cup of coffee takes heat from its surroundings and warms up?

Section 10.4

Using Energy in the Real World

B. Energy as a Driving Force – Energy Spread

• Energy spread – In a given process concentrated energy is dispersed

widely.

– This happens in every exothermic process.

Section 10.4

Using Energy in the Real World

B. Energy as a Driving Force

• Two driving forces:

– Energy spread : why doesn’t a ball roll back up the hill?

– Matter spread : salt dissolving is endothermic, so why does it happen?

Section 10.4

Using Energy in the Real World

B. Energy as a Driving Force – Matter Spread

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

• Example: – Consider a gas trapped as shown . What happens

when the valve is opened?

Section 10.4

Using Energy in the Real World

B. Energy as a Driving Force – Matter Spread

• The gas expands to fill the whole container - no heat energy flows but matter spreads out

Section 10.4

Using Energy in the Real World

B. Energy as a Driving Force - Entropy

• Entropy, S – function which measures the amount of disorder of the components of the universe

An increase in entropy allows an endothermic reaction to happen and enhances an exothermic reaction

Section 10.4

Using Energy in the Real World

B. Energy as a Driving Force – Energy and Matter Spread

• Gibb’s Free Energy, G

– Processes are strongly favored if they involve energy and matter spread.

ΔG = ΔH – TΔS

― A reaction or process is more favored (ΔG is more negative) when ΔH is negative and ΔS is positive

― The Entropy (ΔS) term is more relevant the higher the temperature

Section 10.4

Using Energy in the Real World

B. Energy as a Driving Force

• Second law of thermodynamics

– The entropy of the universe always increases– When did your room last clear itself up?

The “Heat Death of the Universe 1” 2 3 4 5

Section 10.4

Using Energy in the Real World

• Fossil fuel – carbon based molecules from decomposing plants and animals – Energy source for United States

C. Energy and Our World

Section 10.4

Using Energy in the Real World

• Petroleum – thick liquids composed of mainly hydrocarbons

C. Energy and Our World

– Hydrocarbon – compound composed of C and H

Section 10.4

Using Energy in the Real World

• Natural gas – gas composed of hydrocarbons

C. Energy and Our World

Section 10.4

Using Energy in the Real World

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

C. Energy and Our World

Section 10.4

Using Energy in the Real World

• Effects of carbon dioxide on climate

C. Energy and Our World

• Greenhouse effect

Section 10.4

Using Energy in the Real World

• Effects of carbon dioxide on climate

C. Energy and Our World

• Atmospheric CO2

– Controlled by water cycle – Could increase temperature by 10oC

Section 10.4

Using Energy in the Real World

• Alternative energy sources

C. Energy and Our World

– Solar – Nuclear – Biomass – Wind – Synthetic fuels– Wave/tidal– Hydroelectric– Geothermal

-Describe each type of energy source and how it captures or produces energy. - Also list the pros and cons for each source. - Summarize by justifying which energy source you think we should pursue more vigorously and what is the key obstacle to be overcome

Section 10.4

Using Energy in the Real World

Section 10.4

Using Energy in the Real World