2Al+6HCl⇒3H₂+2AlCl₃
<h3>Further explanation
</h3>
Equalization of chemical reaction equations can be done using variables. Steps in equalizing the reaction equation:
• 1. gives a coefficient on substances involved in the equation of reaction such as a, b, or c etc.
• 2. make an equation based on the similarity of the number of atoms where the number of atoms = coefficient × index between reactant and product
• 3. Select the coefficient of the substance with the most complex chemical formula equal to 1
Reaction
Al+HCl⇒H₂+AlCl₃
aAl+bHCl⇒cH₂+AlCl₃
Al, left=a, right=1⇒a=1
Cl, left=b, right=3⇒b=3
H, left=b, right=2c⇒b=2c⇒3=2c⇒c=3/2
the equation becomes :
Al+3HCl⇒3/2H₂+AlCl₃ x2
2Al+6HCl⇒3H₂+2AlCl₃
Heating a substance causes molecules to speed up and spread slightly further apart, occupying a larger volume that results in a decrease in density. Cooling a substance causes molecules to slow down and get slightly closer together, occupying a smaller volume that results in an increase in density.
From: www.middleschoolchemistry.com
I would say the answer is emissions. These are the particles that are not supposed to be present in air but due to the production of different substances from humans daily activities these substances go with the air we breath. Hope this helped.