Q.Low pressure is favourable for which of the following reactions?

Maximum NH3 yield is favoured by low temperature and high pressure.

The reaction N2(g) + 3H2(g) ⇌ 2NH3(g) is exothermic (forward direction releases heat) and reduces the number of gas moles (4 mol reactant gas → 2 mol product gas).

By Le Chatelier's principle:

• Since the forward reaction is exothermic, lowering the temperature shifts equilibrium towards the (heat-releasing) product side, favouring more NH3.
• Since the forward reaction decreases moles of gas, increasing pressure shifts equilibrium towards the side with fewer gas moles, i.e. towards NH3. …

Le Chatelier's principle: adding more of a reactant shifts the equilibrium forward, towards the products, to counteract the increased reactant concentration.

The reaction is: 2H2(g) + CO(g) <=> CH3OH(g)

Le Chatelier's principle states that if a system at equilibrium is subjected to a change in concentration, temperature, or pressure, the equilibrium shifts in the direction that partially counteracts (opposes) that change.

Here, H2 (a reactant) is added, increasing its concentration above the equilibrium value. To counteract this increase, the equilibrium position shifts in the direction that CONSUMES the extra H2 — that is, the forward direction, converting more H2 and CO into CH3OH (the product).

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Low pressure favours the reaction that produces more moles of gas — only the PCl5 dissociation does that.

Le Chatelier's principle: decreasing pressure shifts a gaseous equilibrium toward the side with a greater number of gas moles.

• $PCl_5 \rightleftharpoons PCl_3 + Cl_2$: 1 mol → 2 mol (forward increases moles) → favoured by low pressure.
• $N_2 + 3H_2 \rightleftharpoons 2NH_3$: 4 mol → 2 mol (forward decreases moles) → favoured by HIGH pressure. …

Le Chatelier's principle: adding more of a reactant disturbs equilibrium, and the system shifts to consume the extra reactant, favouring product formation.

Reaction: 2H2(g) + CO(g) <=> CH3OH(g)

According to Le Chatelier's principle, if a system at equilibrium is disturbed by increasing the concentration of a reactant (here, H2), the equilibrium shifts in the direction that consumes the added substance to counteract the disturb …

Le Chatelier's Principle: a stressed equilibrium shifts to oppose/minimize the applied disturbance.

Step 1: The principle applies to any system at dynamic equilibrium (physical or chemical).

Step 2: If concentration of a reactant/product is changed, pressure or volume is changed (for gaseous equilibria), or temperature is changed, the position of equilibrium shifts so as to reduce the effect of that change and restore a new equilibrium. …