Download 1 st Law of Thermodynamics - Mr Hartan`s Science Class

1.3 ENERGY & EQUILIBRIA
ENVIRONMENTAL SYSTEMS & SOCIETIES
SIGNIFICANT IDEAS
1. The laws of thermodynamics govern the flow of
energy in a system and the ability to do work.
2. Systems can exist in alternative stable states or as
equilibria between which there are tipping points.
3. Destabilizing positive feedback mechanisms will drive
systems toward these tipping points, whereas
stabilizing negative feedback mechanisms will resist
such changes.
KNOWLEDGE & UNDERSTANDING
• The 1st law of thermodynamics is the principle of conservation of
energy: energy in an isolated system can be transformed but cannot
be created or destroyed.
• The principle of conservation of energy can be modeled by the
energy transformations along food chains and energy production
systems.
• The second law of thermodynamics states that the entropy of a
system increases over time. Entropy is the measure of the amount of
disorder in a system. An increase in entropy arising from energy
transformations reduces the energy available to do work.
• The second law of thermodynamics explains the inefficiency and
decrease in available energy along a food chain and energy
generation systems.
• An open system, an ecosystem, will normally exist in a stable
equilibrium, either a steady-state or one developing over time (eg.,
succession), and maintained by stabilizing negative feedback loops.
KNOWLEDGE & UNDERSTANDING
• Negative feedback loops (stabilizing) occur when the output of a
process inhibits or reverses the operation of the same process in
such a way to reduce change or deviation from the norm.
• Positive feedback loops (destabilizing) will tend to amplify changes
and drive the system toward a tipping point where a new
equilibrium (new norm) is established.
• The resilience of a system, ecological or social, refers to its
tendency to avoid such tipping points and maintain stability.
• Diversity and size of storages within systems can contribute to their
resilience and affect the speed of response to change (time lags).
• Humans can affect the resilience of systems through reducing
these storages and diversity.
• The delays involved in feedback loops make it difficult to predict
tipping points and add to the complexity of modeling systems.
ENERGY IN SYSTEMS
Energy in Systems are Subject to the
Laws of Thermodynamics
1st Law of Thermodynamics (Principle of Conservation of
Energy:
Energy is neither created nor destroyed but converted
from one form to another. The total energy in the
universe (isolated system) remains constant.
ENERGY IN SYSTEMS
The Second Law of Thermodynamics:
The entropy of an isolated system not in equilibrium will
tend to increase over time. Entropy is the measure of
disorder of a system (refers to the spreading/dispersal
of energy).
ENTROPY
(MORE ENERGY = LESS ORDER)
Over time, all differences in energy in the universe will be evened out
and nothing can change.
ENERGY = WORK + HEAT
(HEAT IS LOW-QUALITY, WASTED ENERGY)
Heat dissipates, without order, to the environment. Heat has high-entropy. Although heat can
warm the environment, it can not power any processes.
• Energy conversions are never 100% efficient. For example, <50% of solar
radiation reaches the Earth’s surface, plants convert only 1-2% to sugars.
Assimilation by consumers is about 10%.
• There will always be a reduction in the amount of energy passed to the next
trophic (feeding) level.
• Life is a battle against entropy and, without constant replenishment of energy,
life would cease to exist.
WHAT IS THE EFFICIENCY OF A LIGHT
BULB?
Efficiency = (work or useful energy produced/energy
consumed) x 100
Based on the above information, what is the efficiency of a standard filament
light bulb (left) vs. a modern, energy-saving bulb?
COMPLEXITY AND STABILITY
The less complex and diverse an ecosystem is, the less
stability and resiliency those systems have.
For example: Monocultures →
• A monoculture is a farming system in which there is only one
major crop. (ex. Potato famine, Ireland, 1845-1848).
EQUILIBRIUM
Equilibrium is the tendency of a system to return to its original state
following a disturbance; at equilibrium, a state of balance exists
among the components of that system.
Types of Equilibria
1.
2.
3.
4.
Steady-state (dynamic) Equilibrium
Static or Stable Equilibrium
Unstable Equilibrium
Stable Equilibrium
Open systems tend to exist in a state of balance or stable
equilibrium. Open systems (ecosystems) tend to avoid sudden
changes. Ecosystems fluctuate (within limits).
STEADY-STATE (DYNAMIC EQUILIBRIUM)
Characteristic of open systems (ecosystems). Continuous
inputs and outputs of energy and matter → The system as
a whole remains in a balanced state.
NEGATIVE FEEDBACK
The process by which any deviations or fluctuations
from an equilibrium are neutralized or counteracted.
The system returns to its previous state after small
fluctuations in the short-term.
EXAMPLES OF STEADY-STATE
EQUILIBRIUM
1. Body Temperature Maintenance:
2. A Mature, Climax Ecosystem:
No long-term changes. Inputs (light, water,
nutrients , gases) and outputs (gases, heat,
salts) balance each other. Climax
Communities look much the same for longperiods of time.
STATIC EQUILIBRIUM
(NO CHANGE OVER TIME)
This cannot occur in living systems as live involves a
constant exchange of energy and matter with the
environment.
Examples Include:
1. The oxygen content of our atmosphere (21% for the
past 2 billion years).
2. A pile of rocks, building or stone wall. They don’t
change their positions for long-periods of time.
UNSTABLE AND STABLE EQUILIBRIUM
Systems can also be stable or unstable. Most systems
display stability by default.
• In stable equilibrium, the system tends to return to the
same equilibrium after a disturbance.
• In an unstable equilibrium, the systems returns to a NEW
equilibrium after a disturbance. (ex. Climate Change)
FEEDBACK LOOPS
Feedback loops can be ►
1. Positive:
• Deviation AWAY from the norm toward a tipping point.
• Change a system to a NEW state.
• Destabilizing as they INCREASE change.
2. Negative:
• Return a system to its original state.
• Homeostatic (maintenance of a stable environment).
• Stabilizing as they reduce change/deviations from
norm.
FEEDBACK LOOPS EXPLAINED
. . . . NEGATIVE FEEDBACK EXAMPLES
• Predator-Prey Interactions & The Lotka-Volterra Model:
• Climate Change:
Rising Global Temperatures ► Melting Ice Caps ► More
water available for evaporation ► More clouds ► More
solar radiation reflected by clouds ► Falling Global
Temperatures.
POSITIVE FEEDBACK EXAMPLES
• Freezing to Death:
Your body temperature falls below 37 degrees.
Shivering/metabolic rate increase but are insufficient.
Metabolic rate falls and continues to fall as enzymes fail to
work. You become lethargic/sleepy. Body cools even further.
You die of hypothermia. Your body is discovered in the
summer.
• Climate Change (again):
Rising global temperatures ►Melting Polar Ice Caps ►Dark
soil exposed/melting of permafrost/methane released ►More
solar radiation absorbed ►Drop in Albedo (reflecting ability
of a surface).
RESILIENCE OF SYSTEMS
Resilience of a system is its ability to return to its initial
state following a disturbance.
Good Resilience: Eucalypt forests of Australia
Bad Resilience: Antibiotic-resistant, pathogenic bacteria.
FACTORS AFFECTING ECOSYSTEM
RESILIENCE
• The more diverse/complex an ecosystem, the more resilient it tends to
be (more interactions between species).
• The greater the species biodiversity of an ecosystem, the greater the
likelihood there is a species that can replace another if it dies (to
maintain equilibrium).
• The greater the genetic diversity within a species, the greater resilience.
A monoculture of wheat or rice can be wiped out by disease if none of
the plants have genetic resistance.
• Species that can shift geographic ranges are more resilient.
• The climate affects resilience. In the Arctic, regeneration/growth of
plants is slow (low temps slow down photosynthesis/cell respiration). In
tropical rain forests, growth rates are fast (light, temp, water are not
limiting factors).
• The faster the rate at which a species can reproduce means recovery is
faster. r-strategists (fast reproductive rate) can recolonize the system
better than K-strategists (slow reproducers).
• Humans can remove or mitigate threats to the system (pollution, invasive
species) – resulting in faster recovery.
TIPPING POINTS
Small (or large) changes in a system can tip the equilibrium beyond a threshold
(tipping) point. Best approach is precautionary.
 An ecological tipping point is reached when an ecosystem
experiences a shift to a new state in which there are significant
changes to its biodiversity and/or services:
• Tipping points involve positive feedback. Positive feedback is selfperpetuating (ex. Deforestation).
• There is a threshold beyond which a fast shift of ecological states
occurs.
• The threshold point cannot be precisely predicted.
• The changes are long-lasting.
• The changes are hard to reverse.
• There is a significant lag-time between the pressures driving change
and the appearance of impacts, creating problems with motivation
and ecological management.
THE PRECAUTIONARY PRINCIPLE
EXAMPLES OF TIPPING POINTS
1. Lake Eutrophication:
2. Extinction of a Keystone Species: Removal of
elephants from a savannah ecosystem can result in
irreversible damage to that system.
3. Coral Reef Death: If ocean acidity levels increase, the
reef coral dies and cannot regenerate.