7: Thermochemistry Flashcards

Question

heat (Q)

Answer 1

transfer of energy as a result of their differences in temperature in J or cal * process function * endothermic when ∆Q\>0 * exothermic when ∆Q\<0 * enthalpy (∆H) is equivalent to heat under constant pressure

Answer 2

q = mc∆T * m=mass * c=specific heat

Answer 3

coffee-cup calorimeter * temperature of the contents is measured to determine heat of reaction

Answer 4

bomb calorimeter * heats of certain reactions (like combustion) can be measured indirectly by assessing temperature change in a water bath around the reaction vessel * q_system = -q_surroundings * abdiatic process because insulation prevents heat exchange

Answer 5

show that phase change reactions do not undergo changes in temperature so you cannot use q=mc∆T during the interval because ∆T=0 * use q=mc∆T in phase * during phase changes, use q=m∆H_{phase change} * solid-liquid boundary... use ∆H_fus * liquid-gas boundary... use ∆H_vap

Answer 6

amount of energy required to raise temperature of one gram of a substance by 1ºC C_H2O(l) = 1 cal/g•K or 4.18 J/g•K

Answer 7

heat capacity = mc * energy required to raise any given amount of a substance by 1ºC

Answer 8

heat changes at constant pressure... state function ∆H_rxn = H_products- H_reactants positive ∆H_rxn corresponds to endothermic process negative ∆H_rxn corresponds to exothermic process

Answer 9

∆H_fº is enthalpy required to produce 1 mole of a compound from its elements in their standard states (most stable state of an element at 298 K and 1 atm) * ∆H_fº of an element in its standard state is zero

Answer 10

∆Hº_rxnis enthalpy change accompanying a reaction being carried out under standard conditions ∆Hº_rxn = Σ∆Hº_{f, products}- Σ∆Hº_{f, reactants}

Answer 11

enthalpy changes of reactions are additive because enthalpy is a state funcion ∆H = ∆H₁ + ∆H₂ + ∆H₃ + ... * applies to ANY state function... like entropy and Gibbs free energy

Answer 12

average energy required to break a particular type of bond between atoms in the gas phase (endothermic) * bond formation has same magnitude of energy but different sign (exothermic)

Answer 13

∆Hº_com is enthalpy change associated with combustion of a fuel * usually hydrocarbon + O2 --\> CO2 + H2O * the larger the alkane reactant, the more numerous the combustion products

Answer 14

energy spontaneously dispreses from being localized to becoming spread out if it is not hindered from doing so * concentration of energy will rarely happen spontaneously in a closed system... work must be done to concentrate energy * ∆S_universe= ∆S_system + ∆S_surroundings \> 0 * ∆Sº_rxn = Σ∆Sº_{f, products}- Σ∆Sº_{f, reactants}

Answer 15

measure of the spontaneous dispersal of energy at a specific temperature ∆S= Q_rev/T Q_rev is heat gained/lost in a reversible process

Answer 16

∆G = ∆H - T∆S * system moves in whichever direction results in a reduction of the free energy of the system * ∆G \< 0 is spontaneous... system is exergonic * ∆G \> 0 is nonspontaneous... system is endergonic * ∆G = 0, system is in a state of equilibrium * ∆H = T∆S \*thermodynamic spontaneity has no bearing on kintetics of reaction... rate of reaction depends on E_a

Answer 17

∆Gº_rxn is free energy change of reactions under standard state conditions ∆Gº_f is free energy change that occurs when 1 mole of a compound in its stardard state is produced from its respective elements in their standard states ∆Gº_rxn = Σ∆Gº_{f, products}-Σ∆Gº_{f, reactants}

Answer 18

∆Gº_rxn= -RTlnK_eq * once a reaction begins, the standard state conditions no longer apple , so for a reaction in progress... ∆G_rxn= ∆Gº_rxn+ RTlnQ

7: Thermochemistry Flashcards

(42 cards)