Why did the candles stop burning when the students placed glass jars over them?

Zinc + lead(ii) nitrate yield zinc nitrate + leadwhat's the chemical equation for this?

How many moles are in 43.9 l of oxygen

Alidded glass container is filled with a colored gas. after a period of time, it is observed that the gas is uniformly spread throughout the box and that the movement has slowed considerably. next, a warm iron plate is carefully placed under the box. why is there resumed movement of the gas in the container?