Module 5 Flashcards
Static equilibrium
Also known as mechanical equilibrium, means the reaction has stopped in other words the system is at rest.
Dynamic equilibrium
In a closed system, a reversible reaction will reach a state of equilibrium. At this point, the rate of the forward reaction is equal to the rate of the reverse reaction. there appears to be no change occurring as the overall concentration of reactions and products stay the same, but at a particle level, reactants and products are changing into each other at the same rate. This is known as dynamic equilibrium - no macroscopic change but microscopic change.
Le Chatelier’s principle
Le Chatelier’s principle states that if a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium shifts to counteract the change to re-establish an equilibrium.
Change in temperature in terms of the collision theory
- Increasing heat energy increases kinetic energy of the particles. This increases their velocity. This also means they are more likely to have sufficient energy to overcome the activation energy needed for the reaction to occur. This increases the frequency of collisions and improves the chances of successful reactions when a collision occurs.
Change in temperature in terms of LCP
- If the forward reaction is exothermic and the temperature is increased the reverse reaction will be favoured to absorb the extra heat.
- Similarly, if the temperature is decreased and the forward reaction is exothermic, the forward reaction will be favoured to produce more heat to bring the reaction back to equilibria.
Change in concentration in terms of the collision theory
- Increasing the concentration of a substance increases the number of particles and hence there is a higher likelihood of reactant particles colliding to form one or more products or vice versa.
Change in concentration in terms of LCP
- If you increase the concentration of reactants in a reaction, the forward reaction will be favoured to produce more products.
- If you decrease the concentration of reactants in a reaction, the reverse reaction will be favoured to produce more reactants.
Change in pressure in terms of the collision theory
- Increasing pressure for gases involves increasing the density or decreasing the volume. Pushing the same number of particles into a smaller space will increase the likelihood of collisions hence increase the rate of reaction.
Change in pressure in terms of LCP
- A change in pressure depends upon the amount of moles in the reaction. If you increase the pressure, and there are more moles of reactants than products, the forward reaction will be favoured in order to ‘decrease’ the pressure.
- If you decrease the pressure, and there are more moles of reactants than products then the reverse reaction will be favoured to ‘increase’ the pressure again.
Explain, in terms of the collision theory, why an increase in temperature of an equilibrium system always favours the endothermic reaction.
Collision theory states that particles must collide with sufficient energy and in the correct orientation to overcome the activation energy barrier. When the temperature is increased, the particles gain kinetic energy. For a chemical reaction, the activation energy barrier for the endothermic reaction is always greater than for the exothermic reaction. Hence, an increase in temperature will affect the percentage of particles able to overcome the endothermic activation energy barrier more than for the exothermic reaction. This will cause the equilibrium to shift in the endothermic direction when the temperature is increased.
Cycad Toxins
Aboriginal and Torres strait islander peoples used a variety of processes to prepare plant materials for food. Some of these foods contain toxic substance’s such as cycasin in cycad seeds. Processes which reduced the concentration of the toxic substances include leeching and fermentation. Cycad seeds were cracked open to extract the kernel. The kernel was ground into a paste and placed in a dilly-bag. The bag was then secured between rocks in a flowing system. The soluble cycasin was leeched out of the paste over several day. Then the paste was dried as used as flour.
Alternatively, the cycad seeds were dropped into a lined pit and covered with soil. Over a period of months, the seeds fermented in anaerobic conditions changing the chemical makeup of the kernels. The seeds are then dug up and consumed.
Lavoisier 1766 theory of acids and bases
After experimenting on oxides of non-metals, Lavoisier came to the conclusion that acids were substances that contained oxygen
L: Many acids, such as hydrochloric acid, do not contain oxygen
Davy 1810 theory of acids and bases
Nothing that hydrochloric acid did not contain oxygen, whilst still acting as an acid. Davy proposed that acids contained replaceable hydrogen atoms
L: This theory did not really have an explanation as to when or how the molecules interacted
Arrhenius 1884 theory of acids and bases
Rather than a substance with replaceable hydrogen atoms, Arrhenius suggested that acids would ionise in water to produce hydrogen ions (H+) and bases would ionise in water to produce hydroxide ions (OH-)
L: - Only applied for aqueous solutions
- Does not account for the behaviour of amphiprotic species that can donate and accept a proton.
Bronsted-Lowry 1923 theory of acids and bases
This theory removed the need for ionisation at all, and thus can explain acids which are acidic without being introduced to water. This definition is that acids are proton donors and bases are proton acceptors.
L: This theory still requires hydrogen atoms to be present within a molecule (e.g: BF3, AICI3) act as an acid without containing any hydrogen.
• A limitation of B-L is that it cannot account for the behaviour of acidic oxides such as SO2 or SO3 and their reaction with basic oxides like CaO.
• could not account for ammonia being a base, as it does not dissociate in water to form hydroxide
