Chemistry Quiz: Chemical Equilibrium

In an equilibrium state, the forward and reverse reactions are still occurring, but at the same rate. This means that the concentrations of the reactants and products remain constant over time, indicating a dynamic balance between the two reactions. The rates of the forward and reverse reactions are equal, resulting in no net change in the amounts of reactants and products.

At equilibrium, the concentrations of reactants and products remain unchanged because the forward and backward reactions are occurring at the same rate. This means that the rate of formation of products is equal to the rate of formation of reactants. If the concentration of any reactant or product is changed, the equilibrium will shift to restore the balance and maintain the concentrations. Similarly, if the temperature, pressure, or volume of the system is changed, the equilibrium will also shift to maintain the concentrations. Therefore, all of the above observations are true for concentrations of reactants and products to remain unchanged at equilibrium.

When a system is at equilibrium, the forward and reverse reactions are still occurring, but at the same rate. This means that the concentrations of reactants and products are no longer changing, as the rates of the forward and reverse reactions are equal. Therefore, the statement "Forward and reverse reaction stop" is incorrect because the reactions are still happening, just at equal rates.

The answer "No units" is correct because the given options are all unit expressions, except for the last one. The first three options have units of concentration, with the first option representing moles per cubic decimeter (mol.dm-3), the second option representing moles squared per cubic decimeter to the power of 6 (mol2.dm6), and the third option representing cubic decimeters per mole (dm3.mol-1). However, the last option, "No units," indicates that there are no units associated with it, suggesting that it is not a valid unit expression.

At a temperature of 25°C, the mixture of H2 and I2 will reach equilibrium. This means that both H2 and I2 will be present in the equilibrium mixture. Additionally, the presence of HI in the equilibrium mixture suggests that a reaction has occurred between H2 and I2 to form HI. Therefore, the correct answer is H2, I2, and HI.

All of the reactions mentioned in the options will not have any units for Kc. This is because the units of Kc depend on the stoichiometric coefficients of the balanced chemical equation. If all the stoichiometric coefficients are dimensionless, then the units of Kc will also be dimensionless. In other words, if the reaction does not involve any substances with units (such as molarity or concentration), then the Kc value will not have any units. Therefore, all of the given reactions will not have any units for Kc.

In an irreversible reaction, equilibrium is never established because the reaction proceeds in one direction only and does not have the ability to reach a state of balance between the reactants and products. Unlike reversible reactions, where equilibrium can be achieved when the forward and backward reactions occur at equal rates, irreversible reactions continue until one or more of the reactants are completely consumed. Therefore, equilibrium is not possible in irreversible reactions.

The question is asking for the reaction in which the equilibrium constant, Kc, has units of mol.dm-3. This indicates that the equilibrium constant is expressed in terms of concentrations of the reactants and products. Option 3 is the correct answer because it is the only option that represents a reaction where the equilibrium constant is defined in terms of concentrations.

Active mass refers to the concentration of a substance in a solution, specifically the mass of the substance per unit volume of the solution. It is commonly expressed in moles per cubic decimeter (dm-3) in a dilute solution. This term is used to describe the amount of a substance that is available for a chemical reaction to occur. The active mass is important in determining the rate of reaction and the equilibrium constant of a chemical reaction.

In a reversible reaction, both reactants can convert into products and vice versa. However, the question specifically asks for the substance that is a product of the reaction. Therefore, the correct answer is A, indicating that substance A is the product of the reversible reaction.