Passage VI
A science teacher lights a new wax candle (which, if left undisturbed, would burn for several hours) in her classroom. She then shows her students a glass jar and asks them to predict what will happen if she places the jar over the lit candle, completely sealing off the candle from the surrounding atmosphere (see figure).
Four students give their viewpoints about why the candle burns and about what will happen to the burning candle once it is under the jar.
Student 1
The candle's flame results from a combustion reaction. When the candle is lit, the flame that lights the candle heats the candle, which causes the candle to give off fumes of wax. The wax fumes act as a fuel that reacts with the O2 present in the air. The reaction gives off energy, which heats the surrounding air, producing a flame. If the jar is laced over the lit candle, the candle will soon stop burning because the O2 , in the air under the jar will be quickly used up.
Student 2
Student 1 is correct except that the fuel reacts with the N2, not with the O2, in the air.
Student 3
None of the components of air are involved in the burning of the candle. When the he candle is lit, the energy from the flame causes the fuel (candle wax fumes) to spontaneously decompose. The heat from the decomposition reaction causes the reaction to continue. Thus, if the jar is placed over the lit candle, the candle will continue to burn until all of the fuel is used up.
Student 4
When the candle is lit, the energy from the flame causes the fuel (candle wax fumes) to spontaneously decompose into a massless substance called heat. None of the components of air chemically react with the fuel, but the O2 present in air is necessary for the sustained decomposition reaction. The O2 is needed because as the heat is produced, the heat must be absorbed for the reaction to continue, and O2 is the only component of air that absorbs heat. When O2 absorbs heat, the O2, is not chemically altered. If the jar is placed over the lit candle, the candle will soon stop burning because the O2, in the air under the jar will quickly become saturated with heat.
31. Based on Student 2’s viewpoint, how will the concentrations (in mg/L) in the jar vary with time, if at all. after the jar is placed over the lit candle?
Your Answer is
Correct Answer is B
Explanation
Student 2 thinks that the reactants are wax fumes and N2, so the content of O2 remains unchanged, and the content of N2 will increase with the Decrease as the reaction progresses