Kinetics and Equilibrium

Question 1

Energy of a Reaction

Answer 1

• Increasing the temperature of the system will make chemical reactions happen faster
  
  • This is because temperature is the average kinetic energy of the particles
• Sometimes bigger chemical molecules, like enzymes, may need to be specifically oriented for a product to occur

Question 2

Chemical Reaction

Answer 2

• A process where reactants are converted into products, but where the reverse process is till possible
• These two reactions have specific rate and there will alway be some equilibrium state where based on the amounts of reacts or products, the forward and reverse rates essentially cancel out

Question 3

Kinetic Energy of a Reaction

Answer 3

• Increasing the temperature of the system will make chemical reactions occur faster.
• This is because temperature is the average kinetic energy of the particle.

Question 4

Orientation of chemical molecules

Answer 4

• Similar to the spider example, sometimes bigger chemical molecules, like enzymes need to be specifically orientated for a product to occur.

Question 5

Spontaneous Reaction

Answer 5

• A reaction that happens without further help or input
• Being spontaneous in a chemical sense means moving from a higher energy state to a lower energy state
  
  • For example, ATP is the energy currency of many biological reactions, but it reacts spontaneously with water to lose phosphate groups, and also lose its energy to its surroundings.
  • This is the reason that ATP is so valuable in out body, as it holds a lot of energy within the molecule, and wants to let that energy go spontaneously.
• Even if there are necessary conditions that need to be satisfied, it still happens on its own if the reaction is spontaneous.

Question 6

Reaction Graph

Answer 6

• The reaction of ATP and water starts with a specific free energy, and that energy is fairly high because the ATP has a bunch of these negative phosphates that are close to each other.
• Water is attracted to the phosphorous in the phosphates, and thats what starts the reaction
• The lone pairs on the oxygen of water, attack the last phosphorous atom in ATP, which creates a compound that we call the transition state, where the water is partially bound to the ATP.

Question 7

Reaction Graph and Transition State

Answer 7

• Transition states are momentary arrangements of atoms with partial bonds.
• But remember that there are a lot of charges oxygens all surrounding the phosphorus.
• This makes for even more repulsion than before, making the transition state very high in energy and unstable.
  
  • Because of this, the energy graph goes up during the transition state of the reaction.
  • This initial increase in energy, that must be gotten past, is called the activation energy.

Question 8

Reaction Graph after Activation Energy

Answer 8

• But then electrons continue to shift, this allows the phosphate oxygen bond to be broken, releases the inorganic phosphate and leaves behind adenosine di-phosphate (ADP)
• The repelling charges move apart, the water’s oxygen bond to the phosphorous is complete and this lets the energy drop down to lower than it originally was before.
• This is the key characteristic that makes a reaction spontaneous - the final free energy state is lower than the initial free energy state.
  
  • But the activation energy that is necessary to get into the transition state, makes a hump in the graph and the bigger the hump on the graph, the slower the reaction proceeds.

Question 9

Catalysts increasing the Rate of Reaction

Answer 9

• Increasing the temperature (or kinetic energy) will generally increase the rate of the forward reaction
• The activation energy is the hump in the graph and one way that we could lower that hump is by using a catalysts since it lowers the activation energy.
• Catalysts: Lower the activation energy of a reaction
• This allows for the reaction to proceed faster to equilibrium
• So in order for something to be counted as a catalyst it can not be consumed or used up in the reaction
• The catalysts doesn’t affect the free energy of the reactants and products
  
  • They can biological catalysts, like enzymes or coenzymes or purely inorganic like metals or cofactors.

Question 10

Biological Enzymes

Answer 10

• Provide a place called an active, to allow the molecules to be arranged in the correct orientation.

Question 11

Biological Enzymes

Answer 11

• Provide a place called an active, to allow the molecules to be arranged in the correct orientation.

Question 12

Elementary Steps

Answer 12

• Multiple steps that occur to allow a reaction to reach completion.

Question 13

Rate-limiting Step

Answer 13

• The slowest step in a reaction that delays the rate of everything else
• For example: Lets consider the reaction of nitrogen dioxide with carbon monoxide
  
  • The one molecule of each combine to form a molecule of nitric oxide and carbon dioxide
  • We would expect that increasing the amount of the reactants will increase the rate of the forward reaction until it reaches equilibrium again
  • It turns out that increasing the concentration of nitrogen dioxide, one of the reacts does increase the rate as we expect
  • However, increase the concentration of carbon monoxide, the other reactant, does not affect the rate at all. (There must be something else happening)
  • While this may seem like its happening in one step it is actually two elementary steps
  • First, two molecules of nitrogen dioxide react to form nitrogen trioxide, and one nitrogen oxide
  • Then, the nitrogen trioxide from the first step combines with carbon monoxide to form the products directly, nitrogen monoxide and carbon dioxide.
  • The first step occurs very slow and the second occurs fast, thus the rate of the reaction is entirely dependent on the first step.
  • The reason that the original net reaction only has one nitrogen dioxide, but there is two in the rate equation is because a compound that appears in the product and reacts of any of the elementary steps can be cancelled out.
    
    • Nitrogen trioxide is an intermediate compound and that gets used in the very next step, so that can be eliminated in the accounting

Question 14

Second Order Reaction

Answer 14

• The sum of all exponents in the rate-law equals two
• From the previous card, this confirms that if we double the concentration of nitrogen dioxide at the start of the reaction, we expect to see a quadruple in the number of collisions

Question 15

Equilibrium

Answer 15

• [K] = [products]/[reactants]
• Chemical equilibrium occurs when the number of particles becoming products is equal to the number of particles becoming reactants.
• Dynamic equilibrium exists once a reversible reaction occurs.
  
  • It is a state where the rate of forward reaction = the rate of reverse reaction
• Le Chatelier’s Principle is that the system will always work to reach equilibrium

Question 16

Kinetic Energy

Answer 16

• Describes the energy that an object posses due to its motion

Question 17

Thermal Energy

Answer 17

• When atoms have kinetic energy
• When something is cold, its particles are moving more slowly, so it has less thermal energy
• When something is getting warmed up, thermal energy increases

Question 18

Potential Energy

Answer 18

• The energy that an object possesses due to its position in relation to a conservative force.
• Types of potential energy:
  
  • Gravitational
  • Electromagnetic
  • Nuclear

Question 19

System

Answer 19

• The part of the universe we’re looking at
• Everything outside the system is called the environment

Question 20

Energy Gaining and lost

Answer 20

• Energy can be lost or gained into two ways
  
  • It can be transferred as work or heat
  • Heat can be transferred into 1 of 3 processes, always from locations of higher temperature to locations of lower temperature
  • 1. Radiation
       * All matter emits light based on its temperature
       * The sun is high frequency, and we are low frequency through infrared
  • 2. Convection
       * Fairly constrained to a specific circumstance, where a fluid id being warmed at the bottom or cooled at the top
       * This differential heating or cooling causes currents to flow in the fluid, mixing it up and spreading the warmed or cooled material more evenly.
  • 3. Conduction
    
    • Work being done as a result of particle collision

Question 21

Net Change in energy

Answer 21

• Calculate the total change of energy of a system by adding up all the energy being transferred
  
  • Delta U = Net change in energy
• When heat energy is lost in a system, the change in energy is negative
• When heat energy enters the system from the environment, the energy change is positive
• If the system expands, the energy change die to work should be negative
  
  • If a system expands, work is done by the system on the surroundings
  • When a system is compressed, work is done on the system by the surroundings.

Question 22

Enthalpy (H)

Answer 22

• Components of enthalpy:
  
  • Internal energy (sum of potential and kinetic energy in a system
  • Energy necessary for a system to take up space
  • We find this energy by multiplying the volume of the system by the pressure of its environment
  • V system x P environment
  • Finding total enthalpy, therefore means adding the internal energy to the product of pressure and volume
    
    • H=U + PV
  • We rarely ever need total enthalpy, rather we need change in enthalpy = delta H
• Key Concept:
  
  • An element’s standard state is a reference point used to calculate its properties at other conditions

Question 23

Bond Breaking

Answer 23

• Whenever bonds are broken, kinetic energy is converted into potential energy to move the atoms apart.
• Energy is REQUIRED to break bonds.
• When hydrogen combusts the bonds between the pairs of hydrogen atoms break, as do the double bonds between all of the oxygen.
  
  • The potential energy of the atoms increases
  • The source of that energy is the thermal energy those atoms possess.
  • The combustion of hydrogen does not only break bonds, it also forms between oxygen and hydrogen, two of these bonds per water molecule.
  • Forming these bonds releases potential energy, turning it back into kinetic energy
• In the case of the combustion of hydrogen, the energy released is MUCH greater than the energy that goes into breaking the bonds
• The reaction of hydrogen and oxygen leads to a change in enthalpy of the system, called the heat of reaction
• This is also a special reaction as it formed water from its constituent elements in their standard states.
• So this reaction is called the formation of water and we would define this reaction’s enthalpy as the heart of formation of water
  
  • In this case, the heat of formation would be negative, because a large amount of potential energy becomes kinetic energy
    
    • This increases the thermal energy, and therefore the temperature of the system greatly.

Question 24

Exothermic Reaction

Answer 24

• Release energy (have a negative enthalpy change), causing an increase in the thermal energy of the system
• Often, the energy leaves the system as heat, part through radiation and the rest through a combination of conduction and convection as the thermal energy transfers into the surroundings (This is known as exothermic reaction)
• Dissolving calcium chloride for example in water is similar
  
  • The result is a decrease in potential energy and an increase in kinetic energy for the particles that make up the system. So the solution becomes warm

Question 25

Endothermic Reaction

Answer 25

• Reactions absorb energy (have a positive enthalpy change), causing a decrease in the thermal energy of a system
• For example, dissolving baking soda in water, heat carries thermal energy into the baking soda solution because thermal energy always moves from areas of high temperature to low.
• There are reactions in which heat goes in, so they have a positive enthalpy change

Question 26

State Functions

Answer 26

• Processes which exhibit path independence
• Since they relate to a change in a property, we only need to know the beginning and the final state to know the change.
• The change in enthalpy is measures only as the difference between the final and initial state.
• When hydrogen burns, it combines with oxygen to produce water vapour
• When it cools does it comes back into a liquid
• Phase changes have their own associated enthalpy change
  
  • Condensation is an exothermic process, energy is released as the molecules bond to one another.
  • The force of attraction between them causes them to gain kinetic energy as they move together
  • In addition, the volume of the system drastically decreases
  • As a result there is a decrease in enthalpy, an exothermic change.

Question 27

Law of Summation

Answer 27

• We can add up the state function changes of different processes happening sequentially to find the net change.

Question 28

Entropy

Answer 28

• A measure of disorder or randomness. The change in entropy (ΔS) is positive when the system moves towards a more disordered state and negative when the system moves towards a less disordered state.
• Chemical reactions tend to proceed in a manner that allows for an increase in the system’s total entropy.
• It is a easier for them to move towards more disorder with a higher entropy than it is for them to become more ordered, with lower entropy
• Solids have the lowest entropy and are the most organized
• Liquids are move disordered than solids because the particles can move past one another so they have higher entropy
• Gases have the highest entropy since they can move freely in any position in their container, meaning that they have the highest entropy.
• temperature also affects entropy, the higher the temperature the more particles of a substance are moving, and the more movement, the more disordered the system is, and the higher the entropy.

Question 29

Gibbs Free Energy (G)

Answer 29

• Take into account both the change in enthalpy and the change in entropy of a system.
• If a reaction results in a decrease in entropy, if things become more ordered, it comes at a cost of energy.
• So even if the process is exothermic, leading to a decrease in HEAT energy of the system, it’s possible that the heat loss is overshadowed by the energy required to decrease the entropy.
  
  • If thats true the reaction will not happen on its own
• The “free” in Gibbs free energy refers to being available, like when you ask if a seat is free before sitting down.
• Changes in entropy can make the energy involved in an enthalpy change become unavailable, or they can make it more available.
• Gibbs is used to describe how much energy is available based on the complete view of both enthalpy and entropy.
• ΔG = ΔH - TΔS
  
  • ΔG = Gibbs Free energy
  • ΔH = Change in enthalpy from the specific reaction
  • T = temperature. in Kelvin
  • ΔS = entropy change of the reaction
• ΔG < 0 : reaction is spontaneous in the forward direction
• ΔG > 0 : reaction is non spontaneous in the forward direction
• ΔG = 0: reaction is at equilibrium

Question 30

Boiling water as an endothermic Process

Answer 30

• Energy is required to break the bonds between water molecules, so without an input of energy it wont happen on its own
• However, boiling water causes an increase in entropy, so despite the process being endothermic it is possible for the reaction to happen if the entropy term in the Gibbs equation is large enough to make the total Gibbs Free Energy negative
• If we wanted to find the temperature where liquid and gaseous water are in equilibrium we would set delta G as zero, plug in the enthalpy change and entropy change values for the reaction, and solve for temperature
• The enthalpy change for water boiling is around 40 thousand joules per mole, and the entropy change is around 110 joules per mole per degree kelvin.