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THE MCAT-CHEM 6
THERMODYNAMICS
| Question | Answer |
|---|---|
| Closed system | exchange of heat and work but not matter with the surroundings |
| isolated system | no exchange of heat, work, or matter with the surroundings |
| open system | exchange of heat, work, and matter with the surroundings |
| What are the characteristics of a state function? | path-independent --> only depend on final and initial states |
| What do state functions include? | enthalpy, entropy, free energy change (delta G), and internal energy change (delta U) |
| Endothermic / exothermic reaction, delta H = | positive / negative |
| What does delta H mean? | change of heat content of a reaction |
| What is standard state? | natural, lowest energy state |
| What is standard state for oxygen? | O2 |
| Why is bond dissociation energy positive? | energy input is required to break bonds |
| Why is enthalpy of formation negative? | energy is released when bonds are formed |
| Calculate bond dissociation energy. | bond dissociation energy of all bonds in reactants - bond dissociation energy of all bonds in products |
| Calculate enthalpy of formation. | enthalpy of all bonds in products - enthalpy of formation of all bonds in reactants |
| T / F. A change in one degree C is the same as a change in 1 K | TRUE |
| heat capactiy | the amt of heat required to raise the temp of something by one degree celsius |
| molar heat capacity | heat capacity per mole ( Joules / mol*C) |
| specific heat capacity | heat capacity per mass (Joules / g*C) |
| How many Joules of energy does it take to raise the temp. of 1 gram of water by 1 degree celsius? | 4.2 J |
| How many joules of energy does one calorie equal? One Calorie? | 4.2 J 4200 J |
| How many calories does one Calorie equal? | 1000 |
| What is free energy? | energy available that can be converted to do work |
| Are all exothermic rxns spontaneous? | NO --> depends on entropy delta G = delta H - T*delta S |
| Do spontaneous rxns happen quickly? | not necessarily |
| Zeroth Thermodynamic law | heat flows from hot objects to cold objects to achieve thermal equilibrium |
| If Ta = Tb, Tb = Tc, then? | Ta = Tc |
| First Thermodynamic Law | Conservation of energy --> change in total energy of a system is equal to contributions from heat and work |
| What does delta E equal to in thermodynamics? | q + w |
| When is q positive? negative? | -heat absorbed into system -heat leaks out of system |
| When is work positive? negative? | -work done on system -work done by system |
| T / F. ALL energy is equivalent even if they are in different forms. | TRUE |
| Second thermodynamic law | universe is increasing in entropy |
| Why is entropy increasing? | irreversibility nature of real processes |
| Room temperature in celsius? body temperature? | 25 / 37 |
| How to convert from celsius to fahrenheit? | C * 1.8 + 32 = F |
| Conduction | heat transfer by direct contact |
| Convection | heat transfer by flowing current through a fluid medium |
| Radiation | heat transfer by EM radiation through emission of photon energy (infrared range) |
| Can radiation occur in a vacuum? | YES |
| heat of fusion | energy input needed to melt something from solid to liquid at constant temperature |
| heat of vaporization | energy input needed to vaporize something from liquid to gas at constant temperature |
| adiabatic process | no heat exchange --> deltaE = W |
| isothermal process | no change in temperature |
| isobaric pressure | pressure is constant, W = P*deltaV |
| isochoric process | volume is constant, W = 0 |
| When does the q = mcdeltaT formula work? | if no phase change is involved |
| Heat of fusion / vaporization is measured in | Joules |
| Heat of fusion equation | q = delta H (fusion) * number moles |
| Heat of vaporization equation | q = delta H (vaporization) * number moles |
| At what temperature does ice melt? Water freeze | 0 degrees C |
| At what temperature does water boil? Steam condense? | 100 degrees C |
| A refrigerator takes in _____ and releases _____. An engine takes in ______ and releases ____. | work / heat heat / work |
| Why does air blown from pursed lips feel cool on the skin? | Expansion of a gas is an endothermic process as it hits the skin |
| Formula for Work with gas expansion / compression | W = - P * deltaV |
| Forming bonds is an _____ process Breaking bonds is an ______ process. | exothermic / endothermic |
| Expansion of a gas is _________. Compression of a gas is ________. | endothermic / exothermic |
| Third Law of Thermodynamics | entropy of a perfect crystal at 0 K is O |
| Relate E, q, and w. | delta E = q + w |
| Favorable at? -S positive, H negative -S negative, H positive -S positive, H positive -S negative, H negative | -all temperatures -at no temperatures -at high temperatures -at low temperatures |
| Rank the enthalpy changes for: melting, evaporation, sublimation | sublimation > evaporation > melting |
| Why does a higher reaction temperature accelerate the rxn? | greater KE within the reactants |
| After reaction completes, what then proceeds? | equilibrium |
| S deals with ____ while G deals with _____. | -entropy -whether or not rxn is spontaneous |
| Does Keq give any information about kinetics? | NO --> only thermodynamics |
| Does the slow or fast step have the highest energy to get over? | slow |
| What defines the rate of a reaction? | activation energy and kinetic region |
| What type of diagram is activation energy read from? | free energy |
| What does deltaGo show? | free energy change when a reaction goes from standard conditions to equilibrium |
| Does enthalpy say anything about favorability of a reaction? | NO |
| In an exothermic reaction, are the products lower or higher than reactants? | lower |
| In an endothermic reaction, are the products lower or higher than the reactants? | higher |
| Do cyclic compounds have more or less entropy than linear compounds? | less --> more rigid and cannot rotate |
| For G and H of formation, an element in its basic form has a value of? | 0 |
| What are the diatomic gases? | Fluorine, Oxygen, Nitrogen, Chlorine, Hydrogen |
| What are the diatomic liquids? | Bromine |
| What are the diatomic solids? | Iodine |
| How many moles of products do formation reactions create? | one mole |
| In an exo rxn, are the bonds formed stronger or weaker than those broken? | stronger |
| What are weaker bonds? On the energy diagram are they high or low? | long bonds / high |
| Does a tertiary carbon form a stronger or weaker bond with hydrogen than a primary carbon? | weaker --> carbocation stability |
| What is the heat capacity fo rwater | 1 cal / g*K |
| How to find the final temp. created from mixing 2 solutions with different temperatures? | mcdeltaT = - mcdeltaT |
| Do solids have higher or lower heat capacities than liquids? | lower --> only vibrational kinetic energy |
| materials with high heat capacities experience smaller or greater temperature increases? | smaller |
| Is the enthalpy of vaporization greater or less than the heat of fusion? | greater |
| strong base + strong acid = | water and neutral salt |
| Why must a lid be used in a calorimetry experiment? | To prevent heat loss from convection and evaporation ** |
| Is warm air less dense or more dense than cool air? | less dense |
| What happens to an object as it radiates photon energy? | object becomes cooler and molecules move less energetically |
| What are 2 formulas for work? | W = F*delta d W = -P * delta V |
| What does it mean when "q" is positive vs. negative? | -positive = heat flows from surroundings into system -negative = heat flows from system into surroundings |
| Thermodynamic Energy Equation | delta E = q + w |
| When does work = 0? | constant volume |
| If a precipitation reaction is favorable, then delta G =? | negative |
| Does water or salt water have the greater heat capacity? | salt water |
| The lower the heat capacity, the greater or less the temperature increase? | greater |
| When something has greater heat capacity, it also has greater? | kinetic energy |
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