Because atoms can join together to form molecules, which in turn form most of the objects around us.
We subtract the enthalpies of the reactants from that of the products:

Since this is < 0, this is an exothermic reaction.
Answer:
the concentration of the reactants
the temperature in heating
The pressure of the gas is expected to increase in accordance to Boyle's law.
<h3>What is Boyle's law?</h3>
Boyle's law states that, the volume of a given mass of gas is inversely proportional to its pressure at constant temperature.
By implication, when the piston is lowered and the volume of the gas is decreased, the pressure of the gas is expected to increase in accordance to Boyle's law.
Learn more about Boyle's law: brainly.com/question/1437490