Question

the reaction shifts left or toward the reactants when hcl is added. which substance(s) increase in concentration during the shift? h₂(g) + cl₂(g) ⇌ 2hcl(g) + 184.6 j h₂ and cl₂ hcl

Explanation:

Step1: Analyze Equilibrium Shift

The reaction is $\ce{H_{2}(g) + Cl_{2}(g)
ightleftharpoons 2HCl(g) + 184.6\ J}$. Adding $\ce{HCl}$ (since $\ce{HCl}$ is a product) will shift the equilibrium to the left (toward reactants) according to Le Chatelier's principle.

Step2: Determine Concentration Change

When the equilibrium shifts left, the forward reaction slows and the reverse reaction (converting $\ce{HCl}$ to $\ce{H_{2}}$ and $\ce{Cl_{2}}$) speeds up. So, the concentrations of the reactants ($\ce{H_{2}}$ and $\ce{Cl_{2}}$) will increase as the reverse reaction produces more of them.

Answer:

$\ce{H_{2}}$ and $\ce{Cl_{2}}$ (the option with "H₂ and Cl₂")