Given that: ΔHof [NO2(g)] = +34.0 kJ mol−1 ΔHof [NO(g)] = +90.0 kJ mol−1 What is the standard enthalpy change of the following reaction: 2NO(g) + O2(g) → 2NO2(g)? A. −112.0 kJ mol−1 B. +112.0 kJ mol−1 C. +124.0 kJ mol−1 D. +248.0 kJ mol−1 Which of the following statements concerning the reaction: CH3CH2OH(l) + 3O2(g) → 2CO2(g) + 3H2O(l) is/are correct? (1) Two C=O bonds are formed during the reaction. (2) One C−C bond is broken during the reaction. (3) Three O−H bonds are formed during the reaction. A(1) only B(2) only C(1) and (3) only D(2) and (3) only Calculate the enthalpy change for the following reaction using the bond enthalpy given below. CH4(g) + Br2(g) → CH3Br(g) + HBr(g) (Bond enthalpy/kJ : C−H = 413, Br−Br = 198, C−Br = 276, H−Br = 366) A. +31 kJ B. -31 kJ C. +857 kJ D. -857 kJ Suppose you are given the following hypothetical reactions: X → Y H = -80 kJ X → Z H = -125 kJ Use Hess's law to calculate the enthalpy change for the reaction Z → Y. A. –205 kJ B. +45 kJ C. –45 kJ D. +205 kJ
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.
Given that: ΔHof [NO2(g)] = +34.0 kJ mol−1
ΔHof [NO(g)] = +90.0 kJ mol−1
What is the standard enthalpy change of the following reaction:
2NO(g) + O2(g) → 2NO2(g)?
A. −112.0 kJ mol−1 B. +112.0 kJ mol−1 C. +124.0 kJ mol−1
D. +248.0 kJ mol−1
Which of the following statements concerning the reaction: CH3CH2OH(l) + 3O2(g) → 2CO2(g) + 3H2O(l) is/are correct?
(1) Two C=O bonds are formed during the reaction.
(2) One C−C bond is broken during the reaction.
(3) Three O−H bonds are formed during the reaction.
A(1) only
B(2) only
C(1) and (3) only
D(2) and (3) only
Calculate the enthalpy change for the following reaction using the bond enthalpy given below. CH4(g) + Br2(g) → CH3Br(g) + HBr(g)
(Bond enthalpy/kJ : C−H = 413, Br−Br = 198, C−Br = 276, H−Br = 366) A. +31 kJ
B. -31 kJ
C. +857 kJ
D. -857 kJ
Suppose you are given the following hypothetical reactions:
X → Y H = -80 kJ
X → Z H = -125 kJ
Use Hess's law to calculate the enthalpy change for the reaction Z → Y. A. –205 kJ
B. +45 kJ
C. –45 kJ
D. +205 kJ
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