Thermochemistry/Thermodynamics Flashcards
System v. Surroundings
System is what we’re observing while the surroundings is everything else.
Describe the three types of systems.
- Open systems- System exchanges energy ( heat or work) and matter with surroundings.
- Closed Systems- System exchanges energy ( heat or work) but not matter with surroundings.
- Isolated systems- system cannot exchange energy ( heat or work) nor matter with surroundings.
Isothermal process
When a change in the system is characterized by constant temperature this changes the equation for the 1st law of thermodynamics to Q=W.
Process
When a system undergoes a change
Adiabatic process
They system does not exchange heat with the surroundings. Change in the internal energy of a system is equal to the work done by the system.
Isobaric process
System contains a constant pressure. Does not change the 1st law of thermodynamics equation.
Isovolumetric process
The volume of the system does not change. Because the volume doesn’t change there’s no work done on the object and therefore there’s no area under the PV graph.
What’s the equation that represents the change in internal energy of a system?
U = Q - W, where Q is the heat added to the system and W is the work done by the system.
Spontaneous v. Nonspontaneous reactions
Spontaneous reactions happens without the input of energy. Nonspontaneous reactions requires input of energy.
Spontaneous reactions doesn’t necessarily mean quick, only catalysts make them quicker.
How can we drive nonspontaneous reactions?
We couple them with spontaneous reactions.
State function v. Process function
State function describes a system’s equilibrium state. The process function describes how the system moves from one equilibrium state to another.
What are the standard conditions?
298K, 1 atm, 1M concentration
What does it mean when we say elements are in their standard states?
They’re in their most stable form
Phase diagrams
Shows the equilibriums and phase stages at different temperatures and pressures.
Vapor pressure
The pressure exerted by gas molecules at the surface of a liquid undergoing evaporation.
Evaporation
When liquid molecules gain enough KE to move into the gaseous phase.
Condensation
Countering pressure from the atmosphere causes some of the gas molecules to turn back into the liquid phase.
Boiling point
The point in which the vapor pressure equals the atmospheric pressure.
What’s the transition from a solid to a liquid? Liquid to solid?
Melting, fusion
Solidifying, crystallizing, freezing
Sublimation V. Deposition
Sublimation is when a solid transitions directly to a gas. Deposition is when a gas directly into being a solid.
Triple point
The point where the 3 phases exist in equilibrium
Critical point
When the densities between the liquid and gas phases are equal we cannot distinguish between the 2 phases.
Enthalpy
The amount of heat in a system. It’s related to the kinetic energy of the molecules.
Zeroth law of thermodynamics
Systems are in thermal equilibrium with each other when their temperatures are the same.
What is the unit of heat?
The joule or calories
1 cal = 4.184 j
The transfer of heat
Heat is the transfer of energy from the hotter object to the cooler object. Calculated via mcat where m = mass, c = specific heat capacity, t= temperature.
Specific heat is the amount of heat required to raise 1 g of a substance 1 degree celsius.
How do we measure the transfer of heat energy?
Via a calorimeter. There are two types: a constant pressure and a constant volume.
Describe the points where heat is not changing on a heat curve?
All the heat being added is being used to overcome the equilibrium between those two phases.
How do we determine the amount of heat absorbed or released using a heat diagram?
For when heat is changing it’s mcat. When during equilibrium it’s ml where l is latent heat.
to find heat absorbed or released across multiple boundaries you add all the heats.
Standard enthalpy of formation
The enthalpy required to produce 1 moles of a compound from elements in their standard states.
Standard heat of reaction
Change in enthalpy of a reaction happening under standard conditions.
To find subtract the enthalpy of the products ( multiplied by their coefficients) by the reactants ( multiplied by their coefficients).
Hess’s law
The enthalpy of reaction can be found by summing all of the enthalpies of the individual elementary reactions.
Whatever we do to the elementary reactions we do to the corresponding enthalpies, we change them to make them like the overall reaction.
Bond dissociation energy
The energy needed to break a covalent bond.
Found by subtracting the enthalpy of the reactants ( bonds broken) by the products (bonds formed).
- Breaking bonds is an endothermic process and forming bonds is a exothermic process.
Standard heat of combustion
The enthalpy changes due to a combustion reaction.
Second law of thermodynamics
Describes entropy. Everything in the universe moves towards disorder.
- Positive entropy- more disorder.
- Negative entropy- less disorder.
How to calculate change in entropy?
We subtract the entropies of the products ( multiplied by the coefficients) by the reactants ( also multiplied by the coefficients).
Gibb’s free energy
Energy available to do useful work.
- Exergonic - spontaneous, negative value.
- Endergonic- nonspontaneous, positive value.
Connection between movement of chemical reaction and free energy.
Exergonic- moving towards equilibrium, spontaneous reaction.
Endergonic- moving away from equilibrium, nonspontaneous reaction.
Standard free energy of formation
Free energy change associated with the formation of 1 mole of a compound from elements in their standard states.
Standard state elements has how much energy?
Elements that’s in their standard states has a free energy change of zero.
Raoult’s law
Law that states that when nonvolatile solutes are added to a solution that the vapor pressure decreases because of the decrease in surface area that the liquid has to escape.
This is accompanied by an increase in the boiling point because it takes a higher temperature to reach the ambient pressure.
What are the state functions and path functions?
The state functions are temperature and enthalpy.
The path function is heat.
What are the thermodynamic properties?
Enthalpy
Entropy
Free energy
Equilibrium
