Equilibrium
Define the difference between static and dynamic equilibrium.
Dynamic equilibrium occurs in closed systems with ongoing reactions, while static equilibrium occurs in systems where no reactions happen.
What are the two main factors required for effective molecular collisions?
Proper direction and sufficient energy.
What is the difference between initial, instantaneous and average rate of reactions?
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What is the role of a closed system in establishing equilibrium?
A closed system prevents the exchange of matter with the surroundings, allowing equilibrium to be achieved.
Write the Kc expression for the reaction N2(g)+3H2(g)⇌2NH3(g)
Kc=[NH3]2/[N2][H2]3
Identify the reaction at equilibrium:
A) K(s)+O2(g)→KO2(s)+ K(s)
B) CaCO3(s)→CaO(s)+CO2(g)
C) N2(g)+H2(g)⇌2NH3
C) N2(g)+H2(g)⇌2NH3(g)
How does a catalyst affect the reaction pathway?
It lowers the activation energy, creating an alternate pathway for the reaction.
What factors affect the rate of a chemical reaction?
Factors include temperature, concentration, surface area, presence of a catalyst, and pressure (for gases).
Give an example of a reversible physical process.
The evaporation and condensation of a liquid in a sealed container.
What is the reaction quotient Qc, and how does it relate to equilibrium?
Qc is the ratio of product to reactant concentrations at any time. Comparing Qc to Kc indicates whether the system shifts forward or backward to reach equilibrium.
Explain the significance of the equilibrium constant Kc
Kc indicates the position of equilibrium. If Kc>1, products are favored; if Kc<1K, reactants are favored.
What is activation energy (Ea), and why is it important?
Activation energy is the minimum energy required for colliding particles to react. It determines whether a reaction will occur by providing the energy needed to break bonds and form new ones.
How can changes in temperature affect the position of equilibrium?
An increase in temperature favors the endothermic reaction, while a decrease in temperature favors the exothermic reaction.
How does Le Chatelier's principle explain the response to increased pressure in a gaseous equilibrium system?
The system shifts to favor the side with fewer moles of gas to reduce pressure.
Calculate Kc for a combined reaction where:
Reaction 1: K1=4.0×10−2
Reaction 2: K2=1.5×10−6
Multiply the constants:
Kc=K1×K2=(4.0×10−2)(1.5×10−6)=6.0×10−8
Why is water often excluded from the Kc expression in equilibrium calculations?
Water is excluded because its concentration is constant in the reaction and does not significantly change.
Why don’t all collisions between particles lead to a chemical reaction?
Not all collisions have sufficient energy (activation energy) or the correct orientation to break bonds and form new ones.
Why does grinding a solid reactant into a powder increase the rate of reaction?
Grinding increases the surface area, exposing more particles to react, which increases the frequency of successful collisions.
How can you experimentally determine the effect of temperature on reaction rate?
Measure the time taken for a visible reaction (e.g., color change or gas evolution) at different temperatures while keeping other variables constant.
Calculate Qc for a reaction if the concentration of reactants is [A]=0.2 M,[B]=0.3 M and products are [C]=0.5 M with the equation A+B⇌C
Q=[A][B][C]=(0.2)*(0.3)/0.5=8.33
Why does the equilibrium constant Kc remain unchanged when a catalyst is added to the system?
A catalyst lowers the activation energy equally for both the forward and reverse reactions. It does not affect the relative concentrations of products and reactants at equilibrium, so Kc remains constant.
How do temperature and the Maxwell-Boltzmann distribution relate to reaction pathways?
Increasing temperature shifts the Maxwell-Boltzmann distribution so more molecules have energy greater than the activation energy (Ea). This increases the number of successful collisions, speeding up the reaction. The pathway remains the same but is more frequently traversed.
Explain why the reaction rate increases with temperature using the kinetic theory.
Higher temperatures increase the kinetic energy of particles, causing them to move faster. This results in more frequent collisions with energy greater than the activation energy, increasing the reaction rate.
Why are gas syringes often used to measure reaction rates involving gas evolution?
Gas syringes provide accurate, direct measurements of gas volume over time, allowing the rate of reaction to be calculated.
For a reaction 2A+B⇌3C, if Kc=4.0K at equilibrium and concentrations are [A]=0.5 M,[B]=0.4 .Calculate [C]
Kc=[C]3/[A]2*[B]