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Energy & Enthalpy
Terms in this set (35)
is work done on or by the system when there is a volume change as measured against an external pressure.
when the sign of the work is positive,
the surroundings do pressure-volume work on the system.
when the sign of the work is negative,
pressure-volume work is done by the system on the surroundings.
H, E, P, & V are _____ _____.
H, is a state property that is related to E, P, & V as H = E + PV
change in internal energy
change in enthalpy, = ∆E + P∆V
product of the pressure & change in volume
1 L ∙ atm
= 101.3 J
∆H is _____ when heat is transferred from the surroundings to the system.
absorb heat from the surroundings & +∆H.
= Vfinal - Vinital
∆H is _____ when heat is transferred from the system to the surroundings.
release heat to the surroundings & -∆H.
instant hand & toe warmers when opened & exposed to air, the reaction 4Fe(s) + 3O₂(g) → 2Fe₂O₃(s)
is exothermic (∆H < 0), releasing heat to the surroundings
instant cold packs are broken upon squeezing, the reaction NH₄NO₃(s) (→ (H₂O)) NH₄NO₃(aq)
is a dissolving process which is endothermic (∆H > 0), absorbing heat from the surroundings
a "cold pack," often used for sports injuries, starts out at room temperature, but squishing the liquid around causes 2 substances to mix that were originally kept separate. when those substances react, the pack quickly begins to feel cold.
a chemical change takes place in a container, making it feel hot to the touch.
campers burn wood to stay warm at night
pocket hand warmers, often used by skiers, start out at room temperature. when the air-tight packaging is opened, a substance contained in a cloth pouch reacts with air, & it quickly begins to feel hot.
solid to liquid
endothermic; melting requires the addition of heat
liquid to gas
endothermic; boiling requires the addition of heat
the process in which a solid transforms into a gas phase without 1st melting to form a liquid phase
solid to gas
endothermic; sublimation requires the addition of heat
gas to liquid
exothermic; condensation requires the removal of heat
liquid to solid
exothermic; freezing requires the removal of heat
the process in which a gas transforms into a solid phase without 1st condensating to form a liquid phase
gas to solid
exothermic; deposition requires the removal of heat
4Al(s) + 3O₂(g) + heat → 2Al₂O₃(s) is a _____ reaction
endothermic because heat is listed on the reactants side of the equation
2H₂(g) + O₂ → 2H₂O(l) + heat
exothermic because heat is listed on the products side of the equation
∆H = energy of the _____ - energy of the _____
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