Week 25 / Thermodynamics 2 Flashcards
(53 cards)
Q: What does Hess’s Law state?
A: Hess’s Law states that the standard enthalpy of a reaction is the sum of the standard enthalpies of the reactions into which the overall reaction can be divided.
Q: What is the implication of Hess’s Law?
[what does it depend on]
A: Hess’s Law implies that enthalpy is a state function, meaning the total change in enthalpy depends only on the initial and final states, not on the path taken.
Q: How can Hess’s Law be applied?
A: Hess’s Law can be applied by breaking down a complex reaction into simpler steps and then summing the standard enthalpies of those individual reactions to find the overall enthalpy change.
Q: What does Hess’s Law allow us to calculate?
A: Hess’s Law allows us to calculate the standard enthalpy change of a reaction even if it cannot be measured directly, by using known enthalpy changes of related reactions.
Q: How did Hess’s Law relate to the catalase reaction discussed earlier?
A: The technique used in the catalase reaction can be expanded by applying Hess’s Law, breaking it down into steps and summing the enthalpies to calculate the total enthalpy change.
What does the standard reaction enthalpy (Δ𝐻 ) represent?
The standard reaction enthalpy is the difference between the standard molar enthalpies of the reactants and products, each weighted by the reaction stoichiometry.
Q: What is the formula for calculating the standard reaction enthalpy?
products - reactants
Q: What are the standard states of reactants and products in a reaction?
Reactants and products are in their standard states, which means they are pure and at 1 bar of pressure.
How do we work indirectly to find the standard reaction enthalpy?
We reference each reactant and product to an imaginary reaction where one mole of it is formed from the constituent elements in their most stable states.
Why is the standard reaction enthalpy calculated indirectly?
It is calculated indirectly because each reactant and product is typically referenced to a reaction where it is formed from its constituent elements in the most stable states.
What is a spontaneous process?
A spontaneous process is one that occurs naturally without the need for external work, such as gases expanding to fill empty spaces or hot objects cooling to the same temperature as their surroundings.
Can spontaneous processes be reversed?
Yes, to reverse a spontaneous process, work must be done upon the system of interest.
What is an example of a spontaneous process?
Examples of spontaneous processes include:
Gases expanding to fill empty spaces
Hydrogen and oxygen combining to produce water
Hot objects cooling to match the temperature of their surroundings
Does spontaneity consider the rate of a process?
No, spontaneity considers whether a process can happen but does not consider how quickly it will happen.
What is the significance of spontaneity in thermodynamics?
Spontaneity in thermodynamics helps determine whether a process can occur naturally, but it doesn’t give any information about the speed of the process.
Q: Do spontaneous processes always move in the direction of lower energy?
A: No, spontaneous processes do not necessarily move in the direction of lower energy.
Q: What happens in an isothermal expansion of a perfect gas into a vacuum?
A: In an isothermal expansion of a perfect gas into a vacuum, there is no overall change in energy. The molecules move at the same speed, but the distance between them changes.
Q: Is energy destroyed in a cooling process?
A: No, in a cooling process, the energy lost by the system is transferred to the surroundings, it is not destroyed.
Q: What happens when two metal blocks, one hot and one cold, are placed in contact in a vacuum?
A: Eventually, the two metal blocks will achieve thermal equilibrium, with heat flowing from the hot block to the cold block until both are at the same temperature.
Q: Does spontaneity involve energy loss or transfer?
A: In spontaneous processes, energy is often transferred (e.g., from a hot body to a cold body), but it is not necessarily lost or destroyed.
Q: What is the tendency of energy and matter in spontaneous processes?
A: Energy and matter have a tendency to disperse in spontaneous processes.
Q: Why is it unlikely for gas molecules to move into one corner of a container?
A: The probability of gas molecules moving into one corner of a container is negligible because they move randomly in all directions.
Q: What happens when hot atoms oscillate in a material?
A: When hot atoms oscillate, they collide with neighboring atoms, transferring energy through these collisions.
Q: How does the dispersion of energy relate to spontaneity?
A: The dispersion of energy, such as the random movement of gas molecules or energy transfer between atoms, is a key characteristic of spontaneous processes.
