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Chem Stack 1
Thermochemistry
| Question | Answer |
|---|---|
| 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
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