Chemistry - Thermochemistry Question with Solution | TestHub
For the reaction, 2NO(g) + O2(g) → 2NO2(g); ΔH = -35.0 kcal at 300 K. If 6.0 moles of NO reacts with 3.0 moles of O2 at constant pressure of 1.0 atm and temperature 300 K to form NO2, then the correct statement(s) is/are (one or more than one correct)
Options:(select one or more)
Answer:
Solution:
Six moles of NO and three moles of O₂ are exactly three times the stoichiometric amounts in the equation. Therefore, the enthalpy change is Δ H = 3(-35.0) = -105 kcal. The heat released at constant pressure is 105 kcal (option b is false).
The number of moles of gas changes from 9 to 6, so Δ ng = -3. The work involved is calculated as |Δ ng| RT = 3 × 2 × 300 = 1800 cal = 1.8 kcal. Since work is done on the system, its magnitude is 1.8 kcal (option a is true).
The change in internal energy is Δ U = Δ H - Δ ng RT = -105 - (-3)(0.6) = -105 + 1.8 = -103.2 kcal. Thus, the internal energy decreases by 103.2 kcal (option c is true, option d is false).
The correct answers are (a) and (c).
