Use the molar DHf° under the formulas to calculate DH°rxn for the equations as balanced: 1. 2B2H6(g) + 3CO2(g) --> 2B2O3(s) + 3CH4(g) ΔH°rxn = _______ kJ ΔH°f = +36 –394 –1274 –75 kJ/mol exo ? endo_thermic 2. 2P2O5 + 2CaC2 -->P4 + 2CaCO3 + 2CO2 ΔH°rxn = _______ kJ ΔH°f = –1505 –59 ___ –1207 –394 kJ/mol exo ? endo_thermic 3. 2Na2CrO4(s) + 10HCl(g) --> 4NaCl(s) + 3Cl2(g) + Cr2O3(s) + 5H2O(l) ΔH°f = –1342 –92 –411 ___ –1140 –286 kJ/mol ΔH°rxn = _______ kJ exo ? endo_thermic
Thermochemistry
Thermochemistry can be considered as a branch of thermodynamics that deals with the connections between warmth, work, and various types of energy, formed because of different synthetic and actual cycles. Thermochemistry describes the energy changes that occur as a result of reactions or chemical changes in a substance.
Exergonic Reaction
The term exergonic is derived from the Greek word in which ‘ergon’ means work and exergonic means ‘work outside’. Exergonic reactions releases work energy. Exergonic reactions are different from exothermic reactions, the one that releases only heat energy during the course of the reaction. So, exothermic reaction is one type of exergonic reaction. Exergonic reaction releases work energy in different forms like heat, light or sound. For example, a glow stick releases light making that an exergonic reaction and not an exothermic reaction since no heat is released. Even endothermic reactions at very high temperature are exergonic.
Use the molar DHf° under the formulas to calculate DH°rxn for the equations as balanced:
1. 2B2H6(g) + 3CO2(g) --> 2B2O3(s) + 3CH4(g) ΔH°rxn = _______ kJ
ΔH°f = +36 –394 –1274 –75 kJ/mol
exo ? endo_thermic
2. 2P2O5 + 2CaC2 -->P4 + 2CaCO3 + 2CO2 ΔH°rxn = _______ kJ
ΔH°f = –1505 –59 ___ –1207 –394 kJ/mol
exo ? endo_thermic
3. 2Na2CrO4(s) + 10HCl(g) --> 4NaCl(s) + 3Cl2(g) + Cr2O3(s) + 5H2O(l)
ΔH°f = –1342 –92 –411 ___ –1140 –286 kJ/mol
ΔH°rxn = _______ kJ
exo ? endo_thermic
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