Thermodynamics Flashcards
A ________ is all reactants and products and the immediate surrounding environment.
system
What is the difference between a closed and open system?
a closed system exchanges energy, but NOT matter with the environment outside the system.
an open system exchanges energy AND matter with the environment outside the system
In any chemical change, the total amount of _________in the universe remains constant, although the ________ of the energy may change
energy, form
Kinetic or potential?
Heat, motion, pressure
kinetic
Kinetic or potential?
bonds, gradients
potential
The energy content of the bonds within the system is_____________.
enthalpy
enthalpy is very (easy/difficult) to measure.
difficult
We tend to measure the change in enthalpy that occurs when reactants form products.
ΔHrxn
We can measure the change in enthalpy by measuring the change in ________ within the system
heat
A reaction that releases heat is ___________.
exothermic
A reaction that absorbs heat is ________.
endothermic
Exothermic or endothermic?
It has a negative ΔH (-ΔH)
exothermic
Endothermic or exothermic?
Positive ΔH (+ΔH)
endothermic
endothermic or exothermic?
Tends to be spontaneous
exothermic
A reaction that neither releases nor absorbs heat is ____________
isothermic
What term describes how spread out energy is in a system.
entropy
An (increase/decrease) in entropy (S) means that the energy in that system is more dispersed.
increase
True or false.
Energy is dispersed or spreads out unless it is hindered from doing so.
True
Why isn’t gasoline exploding all the time? Why does it need a spark?
The reaction is highly exothermic – when gasoline combusts to form water vapour and carbon dioxide, the total chemical bonds go from a higher to a lower energy state (-ΔH)
Reactions that (release/absorb) heat (-ΔH) tend to be spontaneous
release
Reactions that (increase, decrease) entropy (+S) tend to be spontaneous
increase
What does Gibbs Free Energy measure? Does it take into account both entropy & enthalpy?
The energy difference between the products and reactants.
Yes
ΔG = ΔH - TΔS
What equation is this?
Gibbs Free Energy
ΔG = ________
A change in Gibbs Free Energy (change in entropy of the system)
ΔH = ____________
Enthalpy change = heat absorbed or released
TΔS = ____________
Temperature change (in Kelvin)
ΔG is dependent on what 3 factors?
temperature, pH, and relative concentrations of products and reactants
True or false.
Standard Gibbs free energy is calculated at 298 K (room temperature), at a pH of 7, at 1 M of each reactant and product
true
When products and reactants are not both at 1 M, then the reaction is said to be at __________conditions
non-standard
True or false. Even reactions with a fairly large +ΔG can develop into exergonic reactions if the [reactants] is substantially greater than the [products]
True
What is the whole “rationale” for why the body phosphorylates ATP (and dephosphorylates it) as a source of energy currency?
The high-energy phosphodiester bond, when broken, has a negative ΔG
That energy can be coupled to another reaction with a positive ΔG
The net reaction is exergonic…
if the ΔG of ATP is “negative enough” to counteract the endergonic ΔG of the coupled reaction
Most coupled reactions involve enzymes as catalysts
Do enzymes themselves drop the ΔG?
No – enzymes only drop the activation energy
When would the following reactions be spontaneous?
1.) A (-) ΔHrxn and a (+) ΔSsystem
2.) A (+) ΔHrxn and a (+) ΔSsystem
3.) A (-) ΔHrxn and a (-) ΔSsystem
4.) A (+) ΔHrxn and a (-) ΔSsystem
1.) always
2.) sometimes
3.) sometimes
4.) never
