Thermodynamics Flashcards
What are the 3 stores of internal energy (U)
Chemical bond storage
Between molecules (H bonds)
Kinetic energy = motion store
What is temperature identical to in thermodynamics
Kinetic energy of a particle
What does exothermic reaction mean in terms of internal energy of reactants and products
Reactants have more Internal energy = -ve U change
What reaction shows a +internal energy change (products have more Internal energy)
Endothermic reaction
What is the 1st law of thermodynamics
The energy released by a chemical reaction either is used to transfer heat or to do work on surroundings
How would you measure internal energy change?
Measuring heat released (due to the chemical reactions internal energy)
What is enthalpy
It is the heat released = enthalpy of a reaction
How do you work out enthalpy change of a reaction? And the sign
Triangle H = enthalpy change
Energy released - work done = enthalpy change
Why is enthalpy change (H)used more than internal energy (U) change
1- easier to measure than internal energy
2- enthalpy is used to measure Gibbs free energy
What would positive or negative enthalpy (H) change mean?
The heat is absorbed (endothermic) = +
-= heat is released (exothermic)
Which reaction is often favoured?
Exothermic reactions (release heat)
What concept explains why sometimes endothermic reactions are favoured?
Entropy
What is entropy and entropy change sign
Entropy (S) = the disorder of a substance
Entropy change triangle (S)
What is the 2nd law of thermodynamics
Entropy S of a system either increases or remains the same (in terms of disorder you can’t go back to being ordered)
How is solid to gas an example of entropy change
In a solid = ordered
Gas = disordered = most entropic
Why is solid to gas enthalpically unflavoured but entropically favoured
Enthalpically unfavoured because it is endothermic (absorbs heat)
Entropically favoured because more disordered
Do number of micro states increase when entropy /disorder increases?
Yes, in a gas there are multiple micro states (positions available)
How does temperature relate to entropy
Kinetic energy if it drops, there are less micro states available (particles not in motion = no entropy)
What is the 3rd law of thermodynamics
Entropy at 0 temperature = 0 itself
How do you work out Gibbs free energy change?
Triangle G= enthalpy (H) change - (temp x entropy (S) change)
If Gibbs free energy is negative a reaction takes place, why is this
Because if Gibbs free energy is negative , entropy is increased = entropically favoured (disorder)
How do cells sometimes carry out unfavoured reactions?
They couple with favoured
Eg atp synthesis helped by H+ ion transport = favoured
What determines the rate of reaction (collisions and reaction)
The kinetic energy available to overcome an activation energy barrier
How is speed distributed to particles (kinetic energy)
Where they are put in a closed space and collide with eachother transferring energy to particles
What 2 things affect the kinetic energy (speed of a particle)
1- temperature
2- mass (bigger = slower)
How does temperature increase cause increase in rate of reaction
High temp = high kinetic energy
Enough Ke can cause them to go over the barrier
What is the first order reaction
A single molecule which dissociates into 2
What is the second order reaction
Where 2 molecules will collide together to transfer kinetic energy
What is the 3rd order reaction
3 molecules colliding together
How would increasing concentration of molecules in first second and 3rd order increase rate of reaction
More likely collisions / dissociation
How do you work out the equilibrium constant (Keq)
Conc of products (forward) / conc of reactants (backward)
What does a positive Keq mean
More product than reactants in a beaker
What does a negative Keq mean
More reactants than product in beaker
At what point in a reaction is the change in Gibbs energy the lowest
At equilibrium
What would adding reactant or product do to equilibrium
It would push Gibbs energy change from minimum
The reaction counteracts it by either producing more reactant or product = equilibrium
What is le chateliers principle
If something is pushed out of equilibrium eg by adding more reactant , it’s overcome by producing more product
What is free energy
The useful energy left over when wasted work is lost
What is chemical potential of solutes
The free energy of a solute at 1M
And accounting for entropy when mixing
When is chemical potential of solutes the same?
At equilibrium
What is the equilibrium potential
When the concentration gradient and an electrical gradient set up due to movement of ions are the same
How does the Nernst equation find electrical gradient needed to for an equilibrium potential eg of K+
The Nernst potential is the voltage needed to oppose the conc gradient = reach potential equilibrium
What actually allows for an electrical gradient
Movement of ions which causes negative or positive voltage within the cell and this attracts the ions back eg K+
What would it be called if all of the ions involved were at their Nernst potential (potential equilibrium)
Donnan equilibrium
Why is it unrealistic that all ions would be in equilibrium potential (ie no more net movement, conc equal in and out)
The cell would be hypertonic due to other macromolecules in it aswell as ions,
The cell lives in a chemical disequilibrium due to the Na+ k+ pump = prevents cell bursting
What 2 ways is free energy stored due to the increased H conc in the intermembrane of a mitochondria
1- chemical contributions (concentration gradient)
2- electrochemical gradient (the -160mv inside)
What is the effect of the electrochemical gradient and the concentration gradient for free energy called in mitochondria which drives protons into ATPase
Proton motive force
