Hi this question is on my study guide and I want to make sure I get to the right answer and know why.
Explain why the following reaction goes to completion instead of to equilibrium.
Mg(s) + 2HCL(aq) -> MgCl2 (aq) + H2(g) (subscript 2 after MgCl2 and H2)
Reactions go to completion for three (3) reasons.
1. A gas is formed. Here H2 gas is formed.
2. A ppt (a solid; i.e., an insoluble substance) is formed.
3. A weak electrolyte is formed.
Sure! To understand why this reaction goes to completion instead of reaching equilibrium, let's break down the reaction and consider the properties of the reactants and products involved.
The reaction you mentioned is the reaction between magnesium (Mg) metal and hydrochloric acid (HCl) to form magnesium chloride (MgCl2) and hydrogen gas (H2).
When magnesium reacts with hydrochloric acid, the following reaction occurs:
Mg(s) + 2HCl(aq) -> MgCl2(aq) + H2(g)
In this reaction, magnesium (Mg) is a solid, hydrochloric acid (HCl) is an aqueous solution, and magnesium chloride (MgCl2) is also in aqueous form, while hydrogen gas (H2) is a gas phase.
Now, let's look at the factors that contribute to this reaction going to completion:
1. Formation of a gas: One of the key driving forces for a reaction to go to completion is the formation of a gas. In this case, the formation of hydrogen gas (H2) as a product promotes the shift towards the products. Since gas molecules have greater freedom of movement, they escape the reaction mixture and are removed, thus favoring the forward reaction.
2. Strong driving force: The reaction between magnesium and hydrochloric acid is highly exothermic, meaning it releases a considerable amount of energy as heat. This strong driving force makes the reaction energetically favorable, pushing it towards completion.
3. Excess reactant: In this reaction, there is a large excess of hydrochloric acid compared to the amount of magnesium present. Excess reactants can push the reaction towards completion by ensuring that all the available magnesium is consumed.
4. Solubility of product: Magnesium chloride (MgCl2) is a highly soluble salt in water, which means it readily dissolves as soon as it forms. This solubility helps in the forward direction of the reaction.
Combining these factors, the reaction between magnesium and hydrochloric acid goes to completion because of the formation of a gas, the release of a significant amount of energy, the presence of excess HCl, and the solubility of the product.
To summarise, the formation of hydrogen gas, the exothermic nature of the reaction, the excess of hydrochloric acid, and the solubility of magnesium chloride all contribute to the complete conversion of reactants to products, rather than reaching equilibrium.