Answer:
endothermic reaction
Explanation:
It simply means that you are witnessing<u> an endothermic reaction</u>.
An endothermic reaction is one that absorbs heat energy from its surrounding, thereby leaving the reaction vessel with a lower temperature as compared to before the reaction.
It is as opposed to exothermic reactions which are reactions that give off energy in the form of heat to the surrounding, thereby leaving a reaction vessel warmer than before the reaction.
<em>In this case, the formation of ice crystals outside the test tube means that heat energy has been absorbed by the reaction which leaves the vessel a temperature cold enough to activate the formation of ice. </em>
Hg + O2 --> HgO + O
Note that Mercury has a variable valency.
A) can enter from the surroundings, but cannot escape to the surroundings
How difficult it is to change an objects motion. Think of a tablecloth; it takes energy to move it from underneath objects on the table, and it takes energy to move the objects themselves on the table.
