kinetics and entropy Flashcards
kinetics, entropy
The formula for the equilibrium constant
Kc = [products] ^n / [reactants] ^n
What is the reaction quotient?
It is used as part of Le Chatelier’s principle to determine where the equilibrium will shift in a reaction system. It is calculated using; Qc = [products] ^n / [ reactant] ^n (all initial)
Q < K
This means that the product is smaller than the reactant and the equilibrium will shift towards the product
Q = K
This means that the amount of product is equal to the amount of reactant. There will be no shift because the system is already in equilibrium
Q > K
This means that the amount of product is greater than the reactant and the system will shift towards the reactant
What happens when we change the temperature in a reaction system
If it is endothermic and we add heat, it will shift towards the product and if it is exothermic and we add heat, it will shift to the reactant
What happens when we increase pressure and decrease the volume in a reaction system
When we increase pressure, the equilibrium will shift towards the side with the lower amount of moles
What happens when we decrease pressure and increase volume in a reaction system?
When we decrease pressure, the equilibrium will shift towards the side with a higher amount of moles
Does change in volume and pressure affect solids and liquids?
No, changes in volume and pressure have a significant change on only gases. Changes in solid and liquid due to pressure are negligible.
What shift will occur if we add heat to a system with 0Kj
There will be no significant shift because the system is neither exothermic nor endothermic
Consider the following system: 2NO(g) + Cl2(g) --> 2NOCl(g) Which of the following would maximize the yield of nitrosyl chloride (NOCl)? A. Increase pressure B. Decrease pressure C. Pressure has no effect on the yield of NOCl
A.
Increasing pressure will make equilibrium shift to the side with lesser moles. The product has lesser moles than the reactant so increasing pressure will make more NOCl
Consider the following system:
NO(g) + Cl2(g) –> 2NOCl(g) ∆H = -77.4 kJ/mol
Which of the following would maximize the yield of
nitrosyl chloride (NOCl)?
A. Increase temperature
B. Decrease temperature
C. Not enough information
B.
It is an exothermic reaction. Decreasing the temperature will allow the equilibrium to shift to the product
Consider the chemical equilibrium:
A —>
D.
The question says that only the reactant is present initially, this means that there is no product so the quotient is 0.
ie [product] / [reactant]
[0] / [1]
= 0
The following reaction is exothermic: 2 SO2(g) + O2(g) -->2 SO3(g) Which of the following changes will shift the equilibrium towards reactants? A)Raising the temperature B)Adding a solid C)Adding argon D)None of the above
A.
Increasing the temperature will make the exothermic reaction go to the reactants.
Adding a solid will not make a significant change and adding argon would only be significant depending on the volume of the container.
What is entropy in basic terms?
The measure of disorder
Which has the highest entropy and which has the lowest entropy; solid, liquid, gas?
Gas has the highest entropy
Solid has the lowest entropy
The unit for entropy is ___________
J mol-1 k-1 because it is influenced by the temperature
What factors affect entropy?
- Entropy increases when going towards gases (solid < liquid < aqueous < gas)
- Entropy increases as the complexity of the molecule increases
Will entropy increase or decrease? 2 KClO4(s) --> 2 KClO3 (s) + O2 (g)
Entropy will increase because gas is formed
What is the third law of thermodynamics
Entropy is zero for a perfect single atom crystal at zero kelvin
What is entropy 0?
Entropy 0 is the perfect arrangement or ordered state. This is when a crystal forms a perfect array in all directions for infinity. It is approachable but unreachable
