Equilibria (OCR GCSE Combined Science A (Gateway): Chemistry): Flashcards
Exam code: J250
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- FrontEquilibrium
Define reversible reaction.
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Cards in this collection (18)
Define reversible reaction.
A reversible reaction is one in which the products can react to reform the reactants. Both the forward reaction and the reverse reaction can occur.
What symbol is used to show a reversible reaction in a chemical equation?
A reversible reaction is shown using a double half-arrow symbol (⇌). The top arrow points right (forward reaction) and the bottom arrow points left (reverse reaction).
In a reversible reaction, if the forward reaction is exothermic, then the reverse reaction is ...........
In a reversible reaction, if the forward reaction is exothermic, then the reverse reaction is endothermic.
What is dynamic equilibrium?
Dynamic equilibrium is the state reached in a reversible reaction when the rate of the forward reaction equals the rate of the reverse reaction. Concentrations of reactants and products remain constant.
True or False?
Dynamic equilibrium can only be reached in a closed system.
True.
A closed system is one in which no substances can enter or leave. In such a system, a reversible reaction reaches dynamic equilibrium when the rates of the forward and reverse reactions are equal.
At dynamic equilibrium, are the forward and reverse reactions still occurring?
Dynamic equilibrium is the state in a reversible reaction where the rates of the forward and reverse reactions are equal and the concentrations of reactants and products remain constant, even though both reactions are still occurring.
When heating NH4Cl (s), it decomposes into .......... (g) and HCl (g), which recombine on cooling.
When heating NH4Cl (s), it decomposes into NH3 (g) and HCl (g), which recombine on cooling.
In the Haber process, what happens to the rate of the forward reaction as the reaction proceeds?
As the Haber process proceeds, the concentration of reactants (nitrogen and hydrogen) decreases, so the rate of the forward reaction decreases. At the same time, the rate of the reverse reaction increases as ammonia builds up, until both rates become equal at dynamic equilibrium.
True or False?
At dynamic equilibrium, the concentrations of reactants and products are always equal to each other.
False.
At dynamic equilibrium the concentrations of reactants and products remain constant, but they are not necessarily equal. The actual concentrations depend on the specific reaction and conditions.
(Higher Tier Only) What is Le Chatelier's Principle?
Le Chatelier's Principle states that when a change is made to the conditions of a system at equilibrium, the system responds to oppose that change.
(Higher Tier Only) What happens to the position of equilibrium if the concentration of a reactant is increased?
Increasing the concentration of a reactant shifts the equilibrium to the right, towards the products. The system opposes the change by using up the extra reactant to make more product.
(Higher Tier Only) For an exothermic forward reaction, increasing the temperature shifts the equilibrium to the .........., decreasing the yield of product.
(Higher Tier Only) For an exothermic forward reaction, increasing the temperature shifts the equilibrium to the left, decreasing the yield of product.
True or False?
(Higher Tier Only) Changing pressure only affects the equilibrium position if there are different numbers of moles of gas on each side of the equation.
True.
Increasing pressure shifts the equilibrium position towards the side with fewer moles of gas. This reduces the pressure and partially counteracts the change, in accordance with Le Chatelier's principle.
(Higher Tier Only) For the reaction 2NO2 (g) ⇌ N2O4 (g), which direction does equilibrium shift when pressure is increased?
Equilibrium shifts to the right, towards N2O4. Increasing pressure favours the side with fewer moles of gas. There are 2 moles on the left and only 1 on the right.
(Higher Tier Only) How can Le Chatelier's Principle help chemical engineers increase the percentage yield of a reaction?
Le Chatelier's Principle can be used to increase % yield by adjusting concentration, temperature, or pressure. For example, increasing reactant concentration shifts equilibrium to the right; for an exothermic forward reaction, lowering temperature favours the forward reaction; increasing pressure favours the side with fewer moles of gas.
True or False?
(Higher Tier Only) For an endothermic forward reaction, increasing temperature shifts the equilibrium to the right.
True.
Increasing temperature favours the endothermic direction. For an endothermic forward reaction, the system absorbs extra heat by moving towards the products, shifting the equilibrium right.
(Higher Tier Only) Decreasing the concentration of a product shifts the equilibrium to the .........., producing more product.
(Higher Tier Only) Decreasing the concentration of a product shifts the equilibrium to the right, producing more product.
(Higher Tier Only) Why does changing pressure not affect the equilibrium position if there are equal moles of gas on both sides?
If both sides have the same number of moles of gas, increasing pressure raises the rate of both the forward and reverse reactions equally. There is no net shift in the equilibrium position.
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