If a piece of charcoal is taken and set on fire it will evolve CO2 and heat. Charcoal is solid but carbon dioxide is gaseous. This is an example of change of state and evolve of heat during chemical reaction.
Because the rate at which water vapour condenses gets increase slowly to get equal to the rate of evaporation of the water.
Explanation:
When a bottle is partly filled with liquid water is leaves space for vapours to escape and get condensed equally.
When sealed and kept below the lamp the rate of condensation increases due to the empty space in the bottle for getting vapours cool down.
A point arrives when evaporation equates the condensation of the liquid in bottle becomes stable because vapours cannot pass the bottle eventually condense and become liquid.
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