Unit 1 : Thermodynamics Flashcards
What are the differences between an isolated, closed, and open system? Every biological system must be a(n)… (open, closed, isolated system)
Isolated System: Does not exchange matter or energy with its surroundings. These are self contained and mostly theoretical, the only real example is the universe itself.
Closed System: Exchanges energy with its surroundings but matter is contained. For example, hot coffee in a mug — the coffee cannot leave the mug, but the heat energy CAN.
Open System: Exchanges BOTH energy and matter with its surroundings. Every biological system must be an open system in order to bring in nutrients and excrete waste — as well as release heat energy and produce ATP and other forms of energy.
Energy is…
Work is…
Energy is the ability to cause change. So if you think about potential energy, the object is separated from where it wants to be and therefore when released that energy will cause the change of it moving towards that natural position. Kinetic energy is the energy of motion, and so as the object moves it is causing change in its environment and to itself as well.
Work is the change the requires energy, or that is done BY that energy. (Work = Force x change in distance), and it is energy that does this work.
What is the first law of thermodynamics? What is potential and kinetic energy?
1st law of thermodynamics is that ENERGY IS NEITHER CREATED NOR DESTROYED; ALL ENERGY IN THE UNIVERSE IS CONSTANT. So energy CAN change location (inside to outside the cell) and energy CAN change into different forms (potential to kinetic energy), but it can’t just appear or disappear. All energy that enters and leaves a system must come from or go to the surroundings.
Potential energy (Ep): The energy stored due to an object’s position. The further away it is from equilibrium, the more energy it has. Essentially, the more potential it has of moving a further distance and releasing more energy. AKA it’s energy at rest!
Kinetic energy (Ek): The energy of an object’s motion, AKA the energy whilst doing work.
How do we know if a molecule has higher or lower potential energy then another molecule? What happens when a bond changes from non-polar covalent to polar covalent in terms of energy gained/ released?
The potential energy of a molecule is based upon the ARRANGEMENT OF ELECTRONS in the chemical bonds —> and also the bond number (double, triple, etc.) If the two atoms that are bonded have SIMILAR ELECTRONEGATIVITY, then those electrons will be shared relatively evenly, and hence will rest in the middle of the two atoms. So, since those electrons are far away from each atom — and their nuclei which are the parts that the electrons are really attracted to — they will be at a state of high potential energy. If one atom was pulled away, they would immediately cling to the other atom’s nucleus, releasing an immense amount of energy.
If the atoms have different electronegativities, such as C-O and O-H, the electrons will be hovering closely to the more electronegative atom, and therefore will be at a low potential energy. This is because they naturally want to be as close to the strongest nucleus as possible — as this would be their lowest energy state — and so if the less EN atom was released their position would not change much.
So going from a non-polar covalent bond to a polar covalent bond, a lot of energy will be released, as those electrons are going from a higher potential energy state to a lower one.
What is enthalpy? Does the enthalpy of a SYSTEM change when work occurs? What is the symbol for the change in enthalpy, and what variable do we use to measure that change in enthalpy?
Enthalpy is the SUM OF ALL Ek AND Ep IN A SYSTEM! (Not in the entire universe!)
So, when work occurs or something changes in the system, the enthalpy WILL change, because the total energy of a system can change, just not the total energy of the universe. This just means that whatever change occurs in the system, the reciprocal will occur in the surroundings — and this change can be measured indirectly through calorimetry. We look at the loss/gain of HEAT, and say that this is the amount of enthalpy gained/released.
Exothermic means…
Change in H sign will be….
The side of the rxn that the energy will be on is….
Energy of the products is __________________ the energy of the reactants.
Exothermic means that a reaction releases energy from the system to the surroundings. Therefore the products have less enthalpy (Ek and Ep) than the reactants. This means that the change in H sign will be negative, since heat was RELEASED from the system. However, the measured temperature change of the surroundings will be positive/increased, since that heat was RELEASED to the surroundings. And the change in energy of the surroundings HAS TO BE OPPOSITE to the change in energy of the system, according to the first law of thermodynamics.
When writing out the reaction, the energy will be placed on the product side.
The energy of the products will be LESS THAN the energy of the reactants.
Endothermic means…
Change in H sign will be?
Energy will be placed on which side of the reaction?
The energy of the products is _______________________ the energy of the reactants.
Endothermic means that a reaction gains energy in its system. So the change in H sign will be POSITIVE because the enthalpy of the system is increased as this heat/energy is added. When writing out the reaction, energy will be placed on the reactants side — because it is added to the system.
The energy of the products is greater than the energy of the reactants.
In calorimetry, the energy of the surroundings will decreased (and so will the temperature) because heat/energy was ABSORBED from those surroundings to increase the energy of the system and still follow the first law of thermodynamics.
A spontaneous reaction……
Spontaneous reactions ARE NOT ALWAYS ________.
Spontaneity depends on __________, and the ______ law of _________.
The current conditions that need to be focused on to determine spontaneity are… (4)
A spontaneous reaction is a reaction that can happen under the current conditions —> It doesn’t need an input of energy in order to occur (just the activation energy is needed). These current conditions depend not the entropy of the system and surroundings. If the change increases the entropy of the universe overall — maybe the system decreases but this results in a much larger increase of energy for the surroundings — then it DOES follow the 2nd law of thermodynamics and it IS a spontaneous reaction. But all spontaneous reactions still need some activation energy to occur, or else everything would instantaneously burst into flame.
*Spontaneous reactions ARE NOT ALWAYS INSTANTANEOUS!
The current conditions that need to be focused on to determine spontaneity are temperature, pH, atmospheric pressure, and concentration of reactants and products — which are continuously changing throughout the reaction.
What is the second law of thermodynamics? What is entropy? What is the symbol for entropy, and how is it measured?
The second law of thermodynamics states that the total entropy of the universe must always INCREASE! This makes sense because just like concentration gradients, that energy always wants to spread out as much as possible and be at the lowest/most stable state as well. If it is all in one spot, it will be higher potential energy, less stable, and hence will WANT to diffuse out.
Entropy is how dispersed/disorganized the energy of the universe is. So as humans and other organisms grow, they are organizing energy in order to function — which seems to go against this law. However, this is in fact to the case. The entropy of those SYSTEMS may decrease, but the entropy of the universe as a whole will INCREASE! This is because organisms produce a lot of wasteful energy in terms of heat, which is essentially just disorganized, random energy!
Essentially as entropy is increased, the universe is “sharing the love”.
Entropy is measured by this dispersion, so if things get more disorganized or dispersed, then entropy increases and the change in S — how we symbolize entropy — is positive. If things get less dispersed or more organized, then the change in S is negative.
The second law of thermodynamics is referring to the entropy of the system, surroundings, or BOTH always having to increase?
How do we calculate total entropy change?
The 2nd law of thermodynamics is stating that the TOTAL entropy of the universe must always increase. But this doesn’t mean that the entropy of an individual system can’t decrease. If the system decreases in entropy but this causes the surroundings to increase in entropy to a greater degree, then the total entropy will increase and the reaction will be spontaneous!
We calculate this total entropy change with the following formula:
Change in S total = Change in S of system + change in S of the surroundings
What is total entropy and why is it important that we calculate it? Why is it not violation the 2nd law of TD if the system’s entropy decreases?
Total entropy = entropy of the system + entropy of the surroundings
It is important that we calculate this because we can see if the reaction produces a net increase in entropy, and hence if it is spontaneous. Because a reaction can only be spontaneous based on the 2nd law of thermodynamics if the entropy increases, the total entropy change allows us to see if the net entropy change is an increase or a decrease.
It is not a violation of the 2nd law of thermodynamics because even if the entropy of the system decreases, the entropy of the surroundings can increase even more simultaneously or because of that change, and this results in an overall increase in entropy which is then SPONTANEOUS! For example, the human body builds up digested molecules into more complex carbs, fats and proteins to maintain a more organized collection of matter — seems to violate this law. However, in doing this tons of heat is released, and some molecules are broken down in digestion and in burning calories. This disorganized heat energy and other forms only increases the dispersion of energy in the universe, meaning the net change in entropy is an INCREASE.
What is free energy? The _____________ have to have more free energy than the ____________ to have a spontaneous reaction. How are free energy and entropy related (what formula too?) Explain the signs and meaning of this formula for spontaneous and non-spontaneous reactions!
Free energy is a measure of the amount of energy available in a system to do work. If there is not enough free energy in the reactants, then the reaction can’t happen.
The free energy of the REACTANTS must be larger then the free energy of the PRODUCTS in order for a spontaneous reaction to occur — the conditions would then be correct for that reaction to occur at that time.
Free energy and entropy are related by the formula:
(change in G) = -T (change in) S of the system —> where temperature is in Kelvin (never negative).
** So their signs are inversely related. Also this formula is only for the SYSTEM because if it was the total entropy of the universe the entropy could never be negative. This formula is used to calculate changes in the SYSTEM!!
This means that when the entropy increases — in accordance with second law of TD — this sign will be positive, but the Gibbs free energy sign will be negative. When Gibbs free energy is negative, this means that it is LOSING free energy going from R —> P, and so there was a SURPLUS of free energy in the REACTANTS. When this pre-energy is released. It is no longer bound to any bonds, so it is going to want to spread out into the new space it has and the spreading out of energy causes an increase in entropy. Therefore, when entropy is increased, then the Gibbs free energy value will decrease, highlighting that free energy was released to the system.
We can then think of this free energy as DISORDERED ENERGY or ENTROPY!
So when the change in entropy of the SYSTEM is positive, then that means disordered energy was released as that free energy was used, and so the reaction was spontaneous since change in G was negative.
When the change in entropy was negative, energy became more ordered or clustered, and this cannot happen spontaneously. This means for this theoretical reaction the reactants did not have enough free energy to turn into the predicted products, and hence this reaction violates the 2nd law of TD and is NON-SPONTANEOUS!!
What is the full formula for Gibbs Free Energy? What is the enthalpy change of the system proportional to and why?
Gibbs Free Energy = -T change in S total
= -T change in S surroundings + -T change in S system
= change in H - T change in S system
This is because the entropy change of the surroundings is intrinsically related to the enthalpy change of the system. Enthalpy is just a measure of the total energy of the system, and when that changes the variable that is measured is heat.
Heat is just random, scattered energy, and when added to the surroundings it INCREASES the entropy of those surroundings. When absorbed from the surroundings it decreases the entropy of those surroundings.
Therefore, when the change in enthalpy of the system is positive (total energy of the system increases), the entropy change of the surroundings must be negative — because heat was ABSORBED from the environment and therefore disorder was lost. This can be seen by assuming that -T change in S surroundings = change in H of the system. THEY HAVE THE OPPOSITE SIGN!
When the change in enthalpy of the system is negative (total energy of the system decreases and so heat energy is released in the process), disorder through this heat energy was GAINED by the surroundings. This means that the change in entropy of the SURROUNDINGS is POSITIVE, but the change in enthalpy of the system is NEGATIVE, which makes sense with the signs!
So because the change in enthalpy of a system is not isolated, it must impact the entropy of the surroundings which proves the symbiotic relationship between enthalpy of the system and entropy of its surroundings.
Reactions never go to _____________. Instead they will reach a state of ____________ where the proportion of reactants and products are ____________. This state (___________) occurred when the ____________ of the forwards and reverse ___________ are _________. Explain how this state is reached using reaction rates.
Reactions never go to completion. Instead they will reach a state of equilibrium where the proportion of reactants and products are constant — NOT NECESSARILY/NORMALLY EQUAL! This state (equilibrium) occurs when the rate of the forwards and reverse reactions are EQUAL.
Remember, reaction rate is based on the formula
Rate = (concentration for reactant A)(concentration for reactant B).
So we can think of it as having a rate law for both the reactants of the forward reaction and the reactants of the reverse reaction. Then, we can see how those change over time.
At first, when reactants are added there will be no product. Depending on the size of the concentrations, the reaction rate may be fast or slow.
Then, as a net amount of products are formed — since only the forward reaction is occurring — they will begin to react with each other in the opposite direction, in order to produce more of the reactants.
Since the reactants had a head start, they will still be producing a net amount of products, and will not be affected by the added reactants.
But as the product concentration increases, so does the rate for the reverse reaction. That means that the net amount of products produced will begin to decrease. At the same time, the net amount of reactants reacting will begin to decrease. As this graph flattens out, the concentrations of R and P are becoming so that their rates are EQUAL. In this case, for every P produced, an R is produced, and hence the concentrations stay CONSTANT — but not equal to each other.
Relate Gibbs free energy change to equilibrium. Do we want to reach equilibrium in biology? Why/ Why not?
As a spontaneous reaction occurs, the conc. Of R decreases and conc. Of P increases. This means that the change in free energy value is going to continue to increases (become smaller and smaller) until the free energy in the reactants is no longer larger then the free energy in the products — because the amount of reactants is so small. At this point the change in free energy is ZERO, and this is where the reaction can no longer continue in a NET fashion.
IT is at THIS POINT that CHEMICAL EQUILIBRIUM IS REACHED!
But in biology, we never want to reach equilibrium for reactions or else life will end. It is the constant movement TOWARDS equillibrium which powers all life’s systems.
