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Chem Stack 1

Thermochemistry

QuestionAnswer
What is an isolated system? no exchange of heat, work, or matter with the surroundings
What is a closed system? exchange of heat and work, but not matter with the surroundings
What is an open system? exhange of heat, work, and matter with the surroundings
Describe a state function. Path-independent and depends only on the initial and final states
Give examples of state functions. enthalpy, entropy, free energy change, and internal energy change
What else can state function be called? state quantity or function of state
What does conservation of energy mean? The total energy of an isolated system remains constant
What all stays energy constant? The total energy of a closed or open system plus the total energy of its surroundings
What happens to total energy? It is neither gained nor lost but merely transferred between the system and its surroundings
Wheat does endothermic mean? Energy is taken up by the reaction in the form of heat. delta H is positive
What does exothermic mean? Energy is released by the reaction in the form of heat. delta H is negative
What is enthalpy (H)? the heat content of a reaction
What is delta H? the change in the heat content of a reaction.
What does positive delta H mean? heat is taken up during rxn
What does negative delta H mean? heat is released during rxn
What is standard heat of reaction? the change in heat content for any reaction
What is standard heat of formation? the change in heat content for a formation reaction
What is a formation reaction? where a compound or molecule in its standard state is formed from its elemental components in their standard states
What are the conditions of standard state? natural, lowest energy state
How is enthalpy expressed? energy (J) or energy per mol (J/mol)
What is Hess' law of heat summation? sum of product enthalpy changes minus sum of reactant enthalpy changes
What is bond dissociation energy? the energy required to break bonds
Relate standard heat of rxn to bond dissociation energies. Standard heat of rxn = bond dissociation energies of all the bonds in reactants minus bond dissociation energy of all the bonds in products
Relate standard heat of rxn to enthalpy. Standard heat of reaction = enthalpy of formation of all the bonds in products minus enthalpy of formation of all the bonds in reactants
Is bond dissociation energy positive or negative, and why? Positive b/c energy input is required to break bonds
Is the enthalpy of formation of bonds pos or neg, and why? Negative b/c energy is released when bonds form.
What is calorimetry? Measurement of heat changes
What is the specific heat of water? 4.184 J/g * k
What is heat capacity? the amount of heat required to raise the temp of something by 1 degree C
How is molar heat capacity expressed? heat capacity per mol = J/mol * degree C
How is specific heat capacity expressed? heat capacity per mass = J/g * degree C
Can Celcius be replaced by Kelvin here, and why? Yes, b/c a change in 1 degree C is the same as a change in 1 K
How much heat energy is needed to raise the temp of 1 gram of water by 1 degree C? 4.184 J
1 calorie = 4.2 J 1 C = 1000 calories = 4200 J
For water, 1 gram = 1 cubic centimeter = 1 mL
What is entropy? Measure of disorder
How is entropy expressed? energy/temp = J/K (can also be expressed as molar entropy in J/mol * K)
Rank entropies of matter states. Entropy of gas > liquid > crystal states
Which kinds of reactions have a greater increase in entropy? Rxns that produce more mols of gas
What is free energy (G)? the energy available that can be converted to do work
How do you calculate delta G? delta G = delta H - T delta S T = temp in K
What is a spontaneous rxn? A rxn that occurs all by itself
Do spontaneous rxn have pos or neg delta G? negative
Should you assume that exothermic rxns are spontaneous? Why or why not? No, b/c a large, negative delta S can cause it to be nonspontaneous
Should you assume that an endothermic rxn is nonspontaneous? Why or why not? No, b/c a large, positive delta S can make it spontaneous
Should you assume that spontaneous reactions will occur quickly? Why or why not? No, b/c it may take a million years for it to happen, depending on its kinetics
What law deals with the concept of temperature? The zeroth law of thermodynamics
What does the 0th law of thermodynamics say? heat flows from hot objects to cold objects to achieve thermal equilibrium
What is the first law of thermodynamics formula? delta E = q + w
What does the first law of thermodynamics say? conservation of energy the change in total internal energy in a system is equal to the contributions from heat and work
What is delta E the same as? delta U, which is the change in internal energy
What is Q? the contribution from heat
When is Q positive? when heat is absorbed into the system (ie. heating it)
When is Q negative? when heat leaks out of the system (ie. cooling it)
What is W? the contribution from work
When is W positive? when work is done on the system (ie. compression)
When is W negative? when work is done by the system (ie. expansion)
All energy, potential, kinetic, etc has what unit? Joules
Can energy be equivalent in different forms. Yes For example, 1 Joule of mechanical enegy can be converted into 1 Joule of electrical energy (ignoring heat loss).
What does the second law of thermodynamics say? things like to be in a state of higher entropy and disorder
What will happen to the entropy in an isolated system over time? it will increase
What happens when an open system decreases in entropy? It does so at the expense of a greater increase in entropy of its surroundings.
Is the universe as a whole increasing or decreasing in entropy? increasing B/C of the irreversibility nature of real processes, as long as anything occurs, the entropy of the universe increases.
delta S is greater than or equal to what? q/T
What is q? the heat transferred
For reversible processes delta S equals what? q/T
For irreversible processes delta S is > than what? q/T
Are real processes that occur in the world ever reversible? No, so entropy change is always greater than the heat transfer over Temp
Absolute zero in K, C, and F 0, -273, -460
Freezing point of water/melting point of ice in K, C, and F 273, 0, 32
Room temp in K, C, and F 298, 25, 77
Body temp in K, C, and F 310, 37, 99
Boiling point of water/condensation of steam in K, C, and F 373, 100, 212
Formula to convert K to C K = degree C + 273
Formula to convert F to C degree F = degree C X 1.8 + 32
What is conduction? Heat transfer by direct contact. Requires things to touch.
What is convection? heat transfer by flowing current. needs the physical flow of matter
What is radiation? heat transfer by electromagnetic radiation (commonly in the infra-red frequency range). Does not need the physical flow of matter, can occur through a vacuum.
What are other names for heat of fusion? latent heat of fusion, enthalpy of fusion,
What is heat of fusion? the energy input needed to melt something from the solid to the liquid at constant temperature
What are other names for heat of vaporization? latent heat of vaporization, enthalpy of vaporization
What is heat of vaporization? the energy input needed to vaporize something from the liquid to the gas at constant temp
How can you express latent heats as molar values? J/mol
Formula for molor latent heat of fusion Heat of fusion x number of mols of solid
Formula for molar latent heat of vaporization heat of vaporization x number of mols of liquid
Can latent heats be expressed as J/mass? Yes. Energy can be obtained by multiplying the latent heats by the mass of the substance.
Is energy released when a gas condenses into a liquid, or when a liquid freezes into a solid? Yes. The energy released is the same as the energy of their reverse processes.
On a PV diagram, where is the work done shown? it's the area under or enclosed by the curve
What do PV diagrams depict? thermodynamic processes by plotting pressure against volume
What is an adiabatic process? no heat exchange, q = 0. delta E = W
What is an isothermal process? no change in temp, delta T = 0
What is an isobaric process? pressure is constant, W = P delta V
What is an isovolumetric (isochoric) process? volume is constant, W = 0. delta E = q
Calorimetry formula q = mc delta T
What do the terms in colorimetry formula represent? q = heat absorbed/heat input m = mass c = specific heat
The colorimetry formula only works when? Why? when no phase change is involved. Different phases have diff. specific heats, and a phase change requires extra energy such as heat of fusion or heat of vaporization.
How do you work problems that involve phase changes? use the calorimetry equation individually for the different phases. Then take the heat of fusion or vaporization into account.
Created by: forddj