A sealed glass tube containing the equilibrium 2 NO2(g, brown) <-> N2O4(g, colorless), delta H = -57.2 kJ/mol (forward), is placed in three water baths in succession: ice water, room-temperature water, and hot water. Observations: ice bath - tube becomes nearly colorless; room temp - light brown; hot bath - dark brown.
Which observation is most consistent with the forward reaction being exothermic?
- A
color is darker in cold water
- B
color is independent of temperature
- Ccheck_circle
color darkens upon heating, indicating shift toward NO2 (reactant) when T rises
- D
color lightens upon heating
Explanation
For an exothermic forward reaction, raising T shifts equilibrium toward reactants. Reactant NO2 is brown, so dark brown at high T is consistent.