Chemical Equilibrium, Rate, and Electrolysis

Flashcards covering equilibrium constants, Le Châtelier's Principle, electrolysis, catalysts, and collision theory based on the lecture notes.

Equilibrium constant ($K$)

The ratio of the concentration of the products to the concentration of the reactants when a system is at equilibrium.

Equilibrium constant formula

For the reaction $A + B ightleftharpoons C + D$, the formula is K = rac{[C][D]}{[A][B]}, and it is only affected by changes in temperature.

Reaction quotient ($Q$)

A value used to determine how far a system is from equilibrium, using the same formula as the equilibrium constant but with concentrations calculated at any time during a reaction.

Q < K

A condition indicates the reaction system will shift to the right (towards products) to reach equilibrium.

Q > K

A condition indicating the reaction system will shift to the left (towards reactants) to reach equilibrium.

Electrolysis

A chemical process used to drive a non-spontaneous chemical reaction by converting electrical energy into chemical energy.

Electrolytic cell anode

The positive electrode and the site of oxidation.

Electrolytic cell cathode

The negative electrode and the site of reduction.

Molten ionic compound electrolyte

An electrolyte where only the cation and anion are present with no water involved.

Aqueous solution electrolyte

An electrolyte where water is present, meaning hydrogen ($H_2$) or oxygen ($O_2$) may be involved in the reaction.

Secondary cells

Cells that can be recharged; they act as galvanic cells while discharging and as electrolytic cells while recharging.

'Green' hydrogen

Hydrogen produced via polymer electrolyte membrane electrolysis (powered by photovoltaics) or artificial photosynthesis using water oxidation and proton reduction catalysts.

Catalyst

A substance that increases the rate of reaction by offering an alternative reaction pathway with a lower activation energy ($E_a$), without changing the position of equilibrium.

Irreversible reaction

A reaction that only proceeds in the forward direction, indicated by the notation $A + B ightarrow C + D$.

Reversible reaction

A reaction where the conversion of reactants to products and products to reactants occur simultaneously, indicated by the notation $A + B ightleftharpoons C + D$.

Equilibrium

A state in which the forward and backward reactions occur at the same rate, resulting in no net change in the concentration of reactants or products.

Extent of a chemical reaction

A measure defined by how much product is formed when the system reaches equilibrium.

Le Châtelier's Principle

The principle stating that if a change is made to a system at equilibrium, the position of the equilibrium will shift in the direction that counteracts the change.

Collision Theory

A theory stating that for a reaction to occur, particles must collide in the correct orientation and with enough energy to overcome the activation energy barrier.

Reaction rate

A term defining how quickly reactants are turned into products.

Open system

A system that can exchange both matter and energy with its surroundings.

Closed system

A system that contains its reactions and maintains constant concentration by not exchanging matter, though it can still be influenced by temperature.

Collision theory

Collision theory describes the conditions necessary for a chemical reaction to occur.

For successful collisions - reactant molecules must collide, reactant molecules must collide in correct orientation to break bonds, reactant molecules must have sufficient energy to overcome the activation energy ( Ea) the energy required to break the bonds in the reactant molecules to form new bonds.

ways to measure rate of reaction

volume of gas produced, mass lost by the reactants, change in ph, formation of a percipitate, change in temp, change in color

increasing rate of reaction

In any reaction mixture, only a certain proportion of collisions between reactant particles have energy greater than or equal to activation, occur in correct orientation, resulting in a successful collision. To increase RR - the frequency of successful collisions by increasing the number of collisions that can occur at a given time, the proportion of collisions that have energy greater than or equal to activation energy by increasing the energy of all collisions.

5 ways to increase ROR and answers to ROR must include

5 - addition of a catalyst, increase pressure, increase surface area, increase temp, increase concentration. Must identify the change, identify why it occurs, conclude that more successful collisions will occur.

effect of concentration on ROR

the more concentrated a solution is, the greater the number of parties in a given volume of solvent. AN increase in C causes an increase in frequency of collisions which increases SC. leads to an increased rate of reaction.

effect of catalyst on rate of reaction

a catalyst provides an alternative reaction pathway which has a lower Ea than uncatalysed. Means that parties now need to collide with less energy and their collisions will still be successful. Higher proportion of reactant particles will have sufficient energy to overcome the Ea and will undergo a reaction upon collision. Catalysts increase frequency of SC.

effect of pressure on ROR

In a gaseous system, an increase in pressure is the same as a decrease in volume - particles are more concentrated in smaller space which means particles will collide with each other more frequently. c = n/v. more frequency increases SC and leads to an increased rate of reaction.

effect of temp on ROR

An increase in temperature raises the energy of the particles, leading to more frequent and energetic collisions. This enhances the reaction rate as a higher proportion of particles have enough energy to overcome the activation energy barrier. two ways include at higher temp, particles will move faster so collide more frequently. higher collisions = higher number of SC. Also, a higher proportion of the particles have energy greater than or equal to Ea, means higher proportion of collisions are successful.

effect of surface area on ROR

Increasing the surface area of a solid reactant allows more particles to be exposed for collision, resulting in a greater frequency of interactions with other reactants. This leads to an increased rate of reaction as more successful collisions occur.

Catalysts

Substances that increase the rate of a chemical reaction without being consumed in the process. Catalysts work by lowering the activation energy, allowing more particles to achieve the necessary energy for successful collisions. They can be specific to certain reactions and can be in the same phase as the reactants (homogeneous catalysts) or in a different phase (heterogeneous catalysts).

Heterogenous and homogeneous definitions for catalysts

Heterogeneous catalysts are in a different phase than the reactants, while homogeneous catalysts are in the same phase. Both types facilitate chemical reactions by lowering the activation energy.

What is the distinction between reversible and irreversible reactions

Reversible reactions can proceed in both the forward and reverse directions, reaching a state of dynamic equilibrium, while irreversible reactions proceed in one direction only and cannot return to the original reactants.

Difference between rate of reaction and extent of reaction

The rate of reaction refers to the speed at which reactants are converted into products, often measured in terms of concentration change over time, while the extent of reaction indicates the total amount of reactants that have reacted to form products at equilibrium.

Equilibrium and dynamic equilibrium definition with examples

Equilibrium is the state in a chemical reaction where the concentrations of reactants and products remain constant over time, while dynamic equilibrium refers to the condition where both forward and reverse reactions continue to occur at equal rates. For example, in the reaction between nitrogen and hydrogen to form ammonia, equilibrium is achieved when the rates of formation and consumption of ammonia are equal.

Concentration vs time graph and explanation

A concentration vs time graph illustrates how the concentrations of reactants and products change over the course of a reaction, showing the rate of reaction. Typically, it displays a steep decline for reactants and a gradual increase for products until equilibrium is reached.

Extent of reactions

Different reactions proceed to different extents based on factors like temperature, pressure, and concentration, determining how far reactants transform into products before reaching equilibrium.

It is not possible to determine extent of reaction based on equation alone, equilibrium constant K can tell us EOR. For values of K between 10-4 and 10 4, will be a significant amounts of reactants and products still present. For very large values, K bigger than 10 4 is mostly products and for very small values, K smaller than 10 -4 is mostly reactants.

What does the reaction quotient (Q) tell us and what is its formula

The reaction quotient (Q) compares the current concentrations of reactants and products in a chemical reaction to the equilibrium concentrations. Its formula is given by $Q = \frac{[products]}{[reactants]}$. If Q differs from the equilibrium constant (K), it indicates the direction in which the reaction will shift to achieve equilibrium.

what does a higher Q value tell us

A higher Q value indicates that the concentration of products is greater relative to reactants compared to the equilibrium state. This suggests that the reaction will shift to the left, favoring reactants, in order to reach equilibrium.

WHat is the equilibrium constant (K)

The equilibrium constant (K) is a numerical value that indicates the ratio of the concentrations of products to reactants at equilibrium for a given chemical reaction at a specific temperature. A larger K value means a greater proportion of products at equilibrium, while a smaller K indicates a higher concentration of reactants.

Value of K can only change in temperature definition and why

Temp change are the only change that actually alter the energy available to the system. When the energy available to system is altered, the reactants and products adjust to share that energy which can affect the ratio of the products and reactants in a system.

favouring forward reaction for endo or exo

The forward reaction is Endothermic ( enters ) ( where delta H is bigger than 0), increase in temp, increase in extent of reaction and K increases. The forward reaction is exothermic ( exits ) ( where delta H is smaller than 0 ) increase in temp, decrease in extent of reaction and K decreases

equivalence of Q and K

Q = K when the system is at equilibrium, with Q representing the reaction quotient calculated from the current concentrations of reactants and products. If Q < K, the reaction proceeds forward, forward reaction favoured; if Q > K, the reaction proceeds in reverse so backward reaction is favoured.

Maximising yields

To maximise the amount of product obtained, done in 4 ways.

Adding reactant/ removing a product, diluting solutions, changing the pressure of gases or changing the temperature. This changes position of equilibrium which is the relative amounts of reactants and products. These changes shift the equilibrium towards the desired product side, thereby increasing the yield.

La chateliers principle

When a system at equilibrium is subject to a change, the system will adjust itself to partially oppose the effect if that change, to restore equilibrium but cannot be restored back to its original position fully.

How can addition / removal of products / reactants affect the position of equilibrium

The addition of reactants increases their concentration, shifting the equilibrium forward / right to produce more products. Conversely, removing products decreases their concentration, also shifting the equilibrium forward; both adjustments enhance product yield by favoring the direction that counteracts the initial change. Addition of products shifts to the left to consume the added products and favor the formation of reactants, thereby decreasing the yield of products. The removal of reactants decreases their concentration, shifting the equilibrium to the left to produce more reactants and reduce product yield.

How can the change in pressure and volume affect the position of equilibrium

Changes in pressure and volume affect equilibrium in gaseous reactions. Increasing pressure or reducing volume shifts the equilibrium towards the side with fewer moles of gas, while decreasing pressure or increasing volume shifts it towards the side with more moles of gas. This adjustment helps restore equilibrium. According to LCP, the system will shift to the right to partially oppose the increase of pressure by reducing the number of gas particles in the container, a change in pressure will not shift the position of E, the number of particles will remain constant.

Changing pressure by adding an Inert Gas

It does not affect the position of equilibrium if the volume remains constant. The inert gas increases the total pressure but does not alter the partial pressures of the reactants and products, so the equilibrium position remains unchanged.

what does an increase in pressure and reduced volume do

An increase in pressure or a reduction in volume shifts the equilibrium towards the side with fewer moles of gas, helping to counteract the change imposed by the pressure increase. This is in accordance with Le Chatelier's Principle, which states that the system will adjust to minimize the effect of changes in pressure. When pressure is increased at equilibrium, all species increase their concentrations. This shift aims to reduce the total number of gas particles, restoring equilibrium.

How can changing temp affect both the position of equilibrium and value of K

Changes in temperature can shift the position of equilibrium in endothermic or exothermic reactions. For endothermic reactions, increasing temperature shifts the equilibrium to the right, favoring product formation, while decreasing temperature shifts it to the left, favoring reactants. When temp increases, K increases

Conversely, for exothermic reactions, increasing temperature favors the reactants, and decreasing temperature favors the products. When temp increases, K decreases.

Explain how the green chemistry principles of catalysts and designing for energy efficiency address the problem of optimal rate and temperature in industrial reactions

Green chemistry principles promote the use of catalysts to lower activation energies, allowing reactions to proceed more efficiently at lower temperatures. Increasing the ROR without being used up in the process, minimising waste and energy expenditure. Additionally, designing processes for energy efficiency minimizes energy consumption, reducing costs and environmental impact while optimizing reaction rates in industrial settings. Compromising on optimal temp to have a faster reaction, uses less energy despite lower yields.

what is unique about a secondary cell

A secondary cell is rechargeable and can undergo multiple charge-discharge cycles. Unlike primary cells that are designed for single use, secondary cells store energy through reversible chemical reactions.

what considerations would you make in choosing an electrode material for an electrolytic cell

Factors to consider include conductivity, stability, reactivity with electrolytes, and cost. An ideal electrode material should be conductive to facilitate electron transfer, stable to avoid degradation, and inert to the electrolyte to prevent unwanted reactions.

name 2 ways green hydrogen can be produced and give their respective equations

1. Polymer electrolyte membrane electrolysis:
   $2H<em>2O(l) \rightarrow 2H</em>2(g) + O_2(g)$

2. Artificial photosynthesis:
   $6CO<em>2(g) + 6H</em>2O(l) \rightarrow C<em>6H</em>{12}O<em>6(s) + 6O</em>2(g)$