C. Assessment/Applications Test I. True or False. Directions: Read each statement very carefully. Write TRUE if the statement is correct; otherwise write FALSE on the line provided before each number. Hess's Law states that a chemical reaction is independent of the route by which chemical reactions takes place while keeping the same a. initial and final conditions 1. c. initial conditions only d. mid-conditions b. final conditions only The thermochemical equation showing the formation of ammonia, NH3 from its element is: N2 (g) + 3 H2 (g) → 2 NH3 (g); AH = - 92 kJ. a. lost to the surroundings b. gained in the surroundings 2. What happens to the value of AH for a thermochemical reaction if the reaction is reversed? 3. AH is the reciprocal of the original value, and the sign remains the same. b. AH has the same numerical value, and the sign remains the same. AH is the reciprocal of the original value and the sign changes. d. AH has the same numerical value and the sign changes. а. с. Which is NOT true about entropy? a. It is denoted by the symbol S. b. It is a measure of the randomness or disorder of a system. c. It is a measure of how much energy is unavailable for conversion into work. d. A positive value of a change in entropy indicates that the final state is less random than the initial state. 4. 5. Which reaction below is endothermic? a. 2NO2(g) 2 N2O4(g), AH = -58.0 kJ b. PC15(g) = PC13(g) + C2(g), AH = 87.9 kJ N2(g) = 3H2(g) + 2NH3(g), AH = -92.38 kJ d. 2PC13(g) + O2(g) = 2POC13(g), AH = -508 kJ с.
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.
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