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MCAT Chem
Ch. 6
| Question | Answer |
|---|---|
| what is a system | the matter that is being observed. The total amount of reactants and products in a chem. rxn. The solute and solvent used to create a solution |
| isolated system | cannot exchange energy (heat and work) or matter with the surroundings; for example, an insulated bomb calorimeter |
| closed system | the system can exchange energy (heat and work) but not matter with the surroundings. for example, a steam radiator |
| open system | the system can exchange both energy (heat and work and matter with the surroundings. for example, boiling water |
| process | when a system experiences a change in one or more of its properties (concentration of reactant or product, temp, or pressure) associated with changes of state system |
| isothermal process | when the system's temp is constant. constant temp implies that the total internal energy of the system is constant throughout process |
| adiabatic process | no heat is exchanged between the system and the environment. thus heat content of the system is constant throughout the process |
| isobaric process | pressure of system is constant. |
| what are the state functions | temperature, pressure, volume, density, internal energy (E or U), enthalpy(H), entropy(S), and Gibb's free energy (G). when state of system changes from equilibrium one of these must change |
| standard conditions | 25 degrees C, (298K) and 1atm |
| Heat (Q) | the transfer of energy from one substance to another as a result of their differences in temp. heat is a process function, not a state function |
| first law of thermodynamics | change in the total internal energy (delta U) of system is equal to the amount of heat(thermal E) transferred(Q) to system, minus amount of W done by system. DeltaU=Q-W |
| endothermic | process in which system absorbs heat (+DQ)(+DH). |
| exothermic | process in which the system releases heat (-DQ)(-DH) |
| equation for how much heat is released or absorbed in a process | q=mcDT m=mass, c=specific heat, DT=change in temp. |
| enthalpy (H) | way to express heat changes at constant pressure. the change in enthalpy is equal to the heat transferred into or out of the system at constant pressure. DHrxn = Hproducts - Hreactants |
| standard enthalpy of formation | the enthalpy change that would occur if one mole of a compound in its standard state were formed directly from its elements in their respective standard states. DH^0f of an elements in its standard state is 0 |
| standard heat of a reaction | DH^orxn is the hypothetical enthalpy change that would occur if the reaction were carried out under standard conditions. this means that all reactants and products must be in there standard states. |
| Hess's law | enthalpy changes of reactions are additive. When thermochemical equations are added to give net equation for a rxn, the corresponding heats of rxn are also added to give net heat of rxn |
| bond dissociation energy | the average energy that is required to break a particular type of bond between atoms in the gas phase (endothermic process) given as kJ/mol of bonds broken. Bond formation has same magnitude of energy but is positive. |
| second law of thermodynamics | energy spontaneously disperses from being localized to becoming spread out if it is not hindered from doing so. |
| entropy | the measure of the spontaneous dispersal of energy at a specific temperature: how much energy is spread out, or how widely spread it becomes in the process. |
| Gibbs free energy | a measure of the change in enthalpy and entropy as a system undergoes a process. the change in free energy is the maximum amount of energy released by a process, occurring at constant temp and pressure. DG=DH-TDS |
| Delta G and rxns | DG>0 rxn is spontaneous. DG<0 rxn is non spontaneous. DG=0 rxn is in a state of equilibrium thus DH=TDS |
| effects of H and S on G | (-H +S spontaneous at all temps) (+H -S non spontaneous at all temps) (+H +S spontaneous only at high temps) (-H -S spontaneous only at low temps) |
| boiling point | temperature at which the vapor pressure equals the ambient pressure |
| Free energy and Keq | DG^orxn = -RTlnKeq. the greater the value of Keq is, the more possitive the value of its natural log, the more negative the standard free energy change. The more negative the standard free energy change, the more spontaneous the reaction. |
| DGrxn = RTln(Q/Keq) | if ration of Q/Keq is less than one (Q<Keq), then ln will be negative, so the rxn will spontaneously proceed forward to equilibrium. Q/Keq greater than one (Q>keq) ln positive, G+, move reverse until equilibrium reached. Q=Keq then at equilibrium |
| Laws of thermodynamics in equations | DEsyt + DEsurr = DEuniv, DSsys + DSsurr = DSuniv, Suniv = 0 at 0K |
| entropy | a measure of the disorder of a system |
| specific heat | the amount of heat needed to raise the temperature of one unit of mass of a substance by one degree celcius |
| heat capacity | the amount of heat needed to raise the temperature of a substance by one degree centigrade |
Created by:
adam87
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