Download Energy Notes - KLang Science

Energy Notes –
Energy is the capacity to cause change.
 Kinetic: moving object makes other objects move
 pool cue and ball, contraction of leg muscle on bike pedal
 Thermal: random movement (kinetic) of atoms/molecules
 heat
 Potential: static objects energy due to location/structure
 water behind a dam (above sea level)
 Chemical: potential energy available for release in a chemical reaction
 gasoline with oxygen creates an explosion which pushes the pistons & creates exhaust
 food plus oxygen creates energy which produces CO2 and water as a bioproduct
Thermodynamics
Energy is constantly being transformed from one form to another.
 First Law of Thermodynamics: Energy can be transferred and transformed but it cannot be created or
destroyed.
 Plants don’t produce energy from the sun, they transform light energy into chemical energy.
 Second Law of Thermodynamics: Every energy transfer or transformation increases the entropy
(disorder) of the universe.
 The cheetah is converting chemical energy into to kinetic energy but it’s also increasing the
entropy or disorder of it’s surroundings by producing heat and other smaller molecules.
Check-Point/Analysis:
(1) How does the second law of thermodynamics help explain the diffusion of a substance across a membrane?
Second law is the trend toward randomness. Diffusion goes from high concentration (low disorder) to lower concentrations in a
random motion (increasing disorder).
(2) Describe the forms of energy found in an apple as it grows on a tree, then falls, and is digested by someone
who eats it.
Potential energy as it hangs on tree, Chemical energy in the form of sugars/nutrients, Kinetic energy as it falls to the ground, Thermal
energy everything else is lost as heat
(3) If you place a teaspoon of sugar in the bottom of a glass of water, it will dissolve completely over time. Left
longer and eventually the water will disappear and the sugar crystal will reappear. Explain these observations in
terms of entropy.
Sugar crystals being less ordered (disorder increases) as they dissolve. When they re-appear their order is increased (disorder decreases). However,
thinking about the water that evaporated, water moved from ordered liquid state to a less ordered vapor state (meaning the entropy increased for the
water).
Free Energy
Free energy is the portion of a system’s energy that can perform work when temperature and pressure are
uniform.
ΔG = ΔH – TΔS
The change in free energy is equal to the change in enthalpy (total energy of the system) minus the change in
the systems entropy (disorder) and the temperature.
We can use ΔG to predict if a process with occur spontaneously (no energy needed).
ΔG = G Final – G Initial
 –ΔG = spontaneous
 ΔG can only be spontaneous (negative) when there is a loss of energy from the initial state
 –ΔG has less free energy meaning it’s more stable than it was before the reaction
Diver Example:
 At top [high G], less stable (more likely to fall)
 At bottom [low G], more stable (floating)
Dye Example:
 Concentrated drop [high G] to the dispersed
drop [low G] increases the disorder of the
system.
Chemical Example:
 Large molecule to smaller molecule increases
the disorder of the system.
Release/Use Energy
Based on ΔG (free energy change), chemical reactions can be exergonic or endergonic.
Exergonic
 –ΔG (high free energy to lower free energy)
 Releases energy, spontaneously occurs
Endergonic
 ΔG (low free energy to higher free energy)
 Needs energy to complete the reaction
Cellular Respiration
C6H12O6 + 6 O2  6 CO2 + 6 H2O
ΔG = – 686 kcal
Exergonic: For each molecule of glucose, 686 kcal of energy is available for
work in the body. (Spontaneous, no energy needed)
Photosynthesis
6 CO2 + 6 H2O  C6H12O6 + 6 O2
ΔG = +686 kcal
Endergonic: For each molecule of glucose created, 686 kcal of energy is
needed. (Would never be spontaneous, needs energy input)
Metabolism Connection
A living cell is not in equilibrium. There is always a constant flow of materials in and out. If the cell does reach
complete equilibrium then the cell dies because it can no longer create energy.
Energy Coupling – ATP
Energy coupling is the use of an exergonic process to drive an endergonic one.
ATP Hydrolysis – Exergonic
 Water splits ATP into ADP & Pi
 Creates Energy (increasing disorder) ΔG = – 7.3 kcal
ATP Synthesis – Endergonic
 Pi is added to ADP to create ATP
 Uses Energy (decreases disorder) ΔG = + 7.3 kcal
Example of Energy Coupling
In this example, the exergonic process of ATP hydrolysis
is used to drive an endergonic process (the cellular
synthesis of the amino acid glutamine).