Thermodynamics Flashcards
What is the first law of thermodynamics?
Energy cannot be created or destroyed, only converted from one form to another
Define work
Any process that can be used to lift weight
What is work measured in?
Joules
Define heat
The spontaneous transfer of energy from a region of high tempature to a region of lower temperature
What is heat measured in?
Joules
Define temperature
A measure of themal energy of a system, the ability of a system to transfer heat energy to another system
What is enthalpy measured in?
Joules per mole
What is true of enthalpy change if a reaction involves no change in pressure or volume?
Change in enthalpy is the same as the change in internal energy
Define entropy
The measure if distribution of energy throughout the atoms and molecules that make up a system
What is entropy measured in?
Joules per mole per kelvin
What is the second law of thermodynamics?
Any system which is free of external influences becomes more disordered with time
Explain the role of entropy in protein folding
- When a protein chain folds, the solvating water molecules become more disorganised
- This offsets any decrease in entropy due to folding of the protein into a more organised structure
- Net change in entropy is positive
What is Gibbs free energy?
The portion of the enthalpy of a reaction that is avaliable to do work
What are the units of Gibbs free energy?
Joules per mol
What is an exergonic reaction?
A reaction which releases energy to its surroundings
What is an endergonic reaction?
A reaction which absorbs energy from its surroundings
Are exergonic reactions spontaneous?
Yes
What does ΔGº mean?
Free energy chage under standard conditions
What does ΔGº’ mean?
Free energy change under standard conditions at pH 7
How does your body ensure that energy in reactions isn’t just lost as heat?
Energy-releasing chemical reactions are coupled to energy-requiring reactions
When might ΔGº’ be used rather than ΔGº in a calculation?
If a reaction involves the uptake or release of protons
What does ΔG’ represent?
The free energy change associated with a reaction at pH 7 but not under standard conditions
What assumption is made in calculation of ΔG’?
The pH does not devaite from 7 as the reaction proceeds
How can free energy of a reverse reaction be obtained?
By changing the sign
How is the ΔG for a reaction calculated?
Gproducts-Greactants
What does the ΔG tell you about the rate of a reaction?
- Whether a reaction is spontaneous
- Nothing about the rate
What does Kc describe?
The ratio of the concentrations of the products to those reactants when equilibrium has been reached
What units should concentrations be in to calculate Kc?
mol.L-1
What does a value of Kc above 102 indicate?
The reaction lies to the right with the products favoured over the reactants
What does a value of kc between 102 to 10-2?
The reaction lies towards the centre
What does a value of Kc below 10-2 indicate about a reaction?
The reaction lies to the left, favouring reactants
What does a ΔG of 0 represent?
That a reaction is at thermodynamic equilibrium
