- WELCOME TO PART FOUR
OF THE CHEMISTRY VIDEO TUTORIALS GOING OVER REACTION BASICS.
THIS TUTORIAL IS GOING TO FOCUS ON KINETICS.
WHEN WE HEAR THE WORD KINETICS,
WE'RE THINKING ABOUT THE REACTION RATES
AND HOW FAST--
HOW FAST A REACTION CAN OCCUR.
ALL RIGHT, LET'S GET STARTED.
LET'S SEE.
SO WE'VE ALREADY DEFINED THE TERM KINETICS,
AND SO WE'LL LOOK AT REACTION RATES,
ACTIVATION ENERGY,
TRANSITION STATES, AND CATALYSTS.
SO ACTIVATION ENERGY,
WE CAN SYMBOLIZE E SUB A AND TRANSITION STATES
WILL BY SYMBOLIZED WITH THE T DOT S. ALL RIGHTY.
NOW, THE REACTION RATES,
IT'S ALL ABOUT HOW FAST A REACTION PROCEEDS.
SO WHEN WE STUDY THERMODYNAMICS,
WE COULD SAY WHETHER OR NOT A REACTION WAS FAVORED
BUT WE DIDN'T KNOW HOW QUICKLY THAT WOULD HAPPEN.
SO WHAT WE'RE GOING TO LEARN ABOUT NOW IS THAT IF WE
HAVE A LARGE ACTIVATION ENERGY,
WE WILL HAVE SLOW REACTION RATES.
AND IF WE HAVE SMALL ACTIVATION ENERGIES,
WE GET FAST REACTION RATES.
AND SO, WE WILL USE THESE GRAPHS
TO HELP ILLUSTRATE THESE RELATIONSHIPS, RIGHT?
SO AS WE LEARNED FROM COLLISION THEORY,
THE ACTIVATION ENERGY IS THE MINIMUM ENERGY
THAT ARE COMBINED KINETIC ENERGY
OF REACTANTS THAT THEY MUST POSSESS FOR THE COLLISION
TO RESULT IN A REACTION.
SO LET'S LOOK AT THESE TWO REACTIONS HERE,
REACTION A AND REACTION B. SO LET'S DO A LITTLE BIT
OF REVIEW ON OUR THERMODYNAMICS.
FIRST OF ALL, IF WE LOOK AT REACTION A,
IS IT ENDOTHERMIC OR EXOTHERMIC, RIGHT?
SO THAT'S ABOUT THERMODYNAMICS
SO THIS IS A THERMODYNAMICS QUESTION.
AND WE CAN SEE RIGHT HERE
THAT THIS IS WHERE WE LOOK FOR THERMODYNAMICS,
THE DIFFERENCE IN ENERGY BETWEEN REACTANTS AND PRODUCTS
AND WE WOULD DESCRIBE THIS AS EXOTHERMIC
BECAUSE HEAT IS RELEASED
BECAUSE OF THE LOWER ENERGY OF THE PRODUCTS.
AND NOW IF WE LOOK AT REACTION B,
WE SEE THE OPPOSITE SHAPE
AND SO WE CAN GUESS IT'S THE OPPOSITE ONE
AND THAT'S REFERRED TO AS ENDOTHERMIC.
AND HERE, ENERGY MUST BE ABSORBED SO WE PUT A +DELTA H
BECAUSE THE PRODUCTS ARE HIGHER IN ENERGY THAN THE REACTANTS.
ALL RIGHT.
NOW, LET'S GET TO THE NEW STUFF, THE KINETICS.
WHICH REACTION IS FASTER, RIGHT?
SO NOW, RIGHT, THE RATES IS ALL ABOUT THE ACTIVATION ENERGY.
SO THERE'S THE ACTIVATION ENERGY
OF REACTION A AND HERE IS THE ACTIVATION ENERGY
OF REACTION B. SO WHEN WE'RE DRAWING THE ACTIVATION ENERGY,
IT'S THE ENERGY FROM THE REACTANTS
TO THE TRANSITION STATE, RIGHT?
SO THAT'S THE MAXIMUM ENERGY
THAT NEEDS TO BE POSSESSED BY THE REACTANTS
TO GET THE REACTION TO OCCUR.
SO IF WE THINK ABOUT THIS, LET'S SAY WE WERE IN A RACE
AND ONE TEAM GOT TO RACE TO THE TOP OF THIS HILL, RIGHT?
ONE TEAM STARTED HERE AT THE REACTANTS
AND ONLY HAD TO RACE TO THE TOP OF THIS HILL
AND THEN THE COMPETITORS HAD TO START WAY DOWN HERE
AND RACE ALL THE WAY TO THE TOP OF THE HILL, RIGHT?
WHO'S GOING TO GET THERE FASTER?
WELL, DEFINITELY, IT'S GOING TO BE REACTION A, RIGHT?
SO WE CAN THINK OF IT AS A SMALLER HILL
TO CLIMB OR A SMALLER ACTIVATION ENERGY,
RIGHT, THAT CREATES THE FASTER REACTION RATE.
ALL RIGHTY.
SO LET'S GO TO THE NEXT PAGE NOW
AND LOOK AT WHAT FACTORS AFFECT REACTION RATES.
SO GET THAT CENTERED, THERE WE GO. OKAY.
SO THERE ARE THREE MAIN CONSIDERATIONS FOR--
THAT AFFECT REACTION RATES.
THE CONCENTRATION OF THE REACTANTS
AND REMEMBER THAT WE'LL USE THESE SYMBOLS HERE,
THE BRACKETS, TO REPRESENT CONCENTRATION
OR THE TEMPERATURE OR THE PRESENCE OF A CATALYST.
THAT'S ENOUGH THERE.
OKAY. ALL RIGHTY.
SO THERE'S THE THREE FACTORS.
NOW, WE'LL GO THROUGH THEM SYSTEMATICALLY.
SO WE'LL START WITH THE CONCENTRATION.
AND SO I THINK THIS ONE IS PRETTY INTUITIVE AND LOGICAL.
AS WE INCREASE THE CONCENTRATION OF THE REACTANTS,
WE'RE GOING TO INCREASE THE REACTION RATES, RIGHT?
IT WILL ALL LINK BACK TO COLLISION THEORY.
THE MORE REACTANTS,
THE MORE LIKELY THEY'RE GOING TO COLLIDE.
SO IT'S A PROBABILITY THING.
AND OF COURSE, IF WE LOSE REACTANTS,
IF REACTANTS ARE LOST,
WHERE THE AMOUNT OF REACTANTS IS DECREASED,
THAT'S GOING TO SLOW DOWN THE REACTION RATE.
THERE'S LESS CHANCE OF COLLISIONS
IF THERE'S LESS REACTANTS.
NOW, THAT WE'VE LOOKED AT IT AND DESCRIBED IT VERBALLY.
LET'S LOOK AT WHAT THIS MEANS GRAPHICALLY.
ALL RIGHT. SO LET ME SEE LIKE HOW MUCH OF THIS I CAN GET.
WELL, WE'RE CLOSE. OKAY.
SO HERE WE HAVE A REACTION OF DINITROGEN PENTOXIDE DECOMPOSING
INTO NITROGEN DIOXIDE AND OXYGEN
AND SO LET'S LOOK AT HOW THE CONCENTRATION
OF THE DINITROGEN PENTOXIDE,
RIGHT, NOTICE
AS THE REACTION PROCEEDS THAT THE CONCENTRATION IS LOWERED.
SO NOW LET'S CONNECT THIS TO THE REACTION RATE.
SO WE SEE WHEN THE--
WHEN THE CONCENTRATION
OF THE DINITROGEN PENTOXIDE IS HIGH,
RIGHT, WE'RE GETTING A LARGE CHANGE IN CONCENTRATION,
RIGHT, BECAUSE THE RATE IS FAST.
I GUESS WE COULD PUT THAT IN THERE. OKAY.
IF WE LOOK LATER, LATER IN THE REACTION PROGRESS,
AS THE DINITROGEN PENTOXIDE REACTION DECREASES,
NOW IF WE LOOK AT THE CHANGE,
WE SEE THAT IT'S MUCH SMALLER, RIGHT?
WE GET A SMALLER CHANGE IN OUR REACTION RATE
AND THE WAY THAT WE'RE MEASURING
THE REACTION RATE IS BY THE CHANGE IN OUR REACTANT.
SO WE SEE THAT THERE'S A SMALLER CHANGE IN OUR REACTANT,
RIGHT, BECAUSE THE RATE IS SLOWER.
SO THIS GRAPH ILLUSTRATES THAT THE CONCEPT
OF CONCENTRATION AND HOW IT AFFECTS REACTION RATES AND THEN
FOR THOSE OF YOU THAT LIKE INFORMATION IN A TABLE FORM,
WE CAN LOOK AT IT RIGHT HERE, A THIRD PRESENTATION.
IF WE LOOK RIGHT AT THE HIGHEST CONCENTRATION,
WE HAVE THE FASTEST RATE AND AT THE LOWER CONCENTRATION,
WE HAVE A MUCH SLOWER RATE.
SO, AND THEN I DO, I PUT THOSE COLOR COORDINATING.
ALL RIGHT. OKAY.
SO THAT SUMMARIZES THE EFFECTS
OF CONCENTRATION ON REACTION RATES.
NOW, LET'S SEE WHAT HAPPENS WITH TEMPERATURE.
SO THE CONCEPTS
IN THIS TUTORIAL ARE HEAVILY BASED ON THE COLLISION THEORY.
SO IF SOME OF THE TERMS OR CONCEPTS I'M DESCRIBING
ARE UNFAMILIAR TO YOU,
IT'D BE A GOOD IDEA TO GO BACK
OVER THE COLLISION THEORY VIDEO TUTORIAL.
ALL RIGHT.
REMEMBER COLLISION THEORY.
SO AS WE INCREASE THE TEMPERATURE,
WHAT HAPPENS IS, RIGHT,
WE INCREASE THE KINETIC ENERGY OF THE SYSTEM
AND SO THAT INCREASES THE ENERGY OF THE COLLISIONS.
IT ALSO INCREASES THE NUMBER OF COLLISIONS.
SO WITH THIS LOGIC,
WE CAN SEE THAT AS WE INCREASE THE TEMPERATURE,
WE ARE GOING TO INCREASE THE REACTION RATE.
THERE IS A RULE OF THUMB FOR EVERY 10 DEGREES
THAT WE INCREASE THE REACTION TEMPERATURE,
THE RATE DOUBLES.
ALL RIGHTY.
AND SO THIS IS AN EXAMPLE OF WHY WE REFRIGERATE OUR FOOD, RIGHT?
WE COOL OUR-- OOPS.
WE COOL OUR FOOD TO SLOW DOWN THE RATE OF SPOILAGE, RIGHT?
WE'RE SLOWING DOWN THOSE REACTIONS INSIDE THE FOOD
THAT CAUSE OUR FOOD TO ROT.
OKAY. AND THEN LET'S SEE,
WHAT ELSE CAN WE TALK ABOUT HERE? OH, OKAY.
AND THEN ANOTHER THING RELATED TO TEMPERATURE IS THAT--
FOR OUR HEALTH,
OUR BODIES NEED TO MAINTAIN CONSTANT TEMPERATURE.
SO IN THE LABORATORY,
IT'S REALLY COMMON TO INCREASE THE TEMPERATURE OF A REACTION
TO MAKE IT GO FASTER BUT INSIDE OUR BODY,
WE DON'T HAVE THAT LUXURY.
WE DON'T WANT TO BOIL OUR CELLS, RIGHT?
SO SINCE WE CANNOT USE HEAT TO INCREASE THE PATHWAYS,
WE NEED A DIFFERENT STRATEGY.
AND THIS STRATEGY IS CATALYSTS.
SO THAT LEADS US TO THE THIRD FACTOR
THAT CAN AFFECT REACTION RATES.
SO LET'S TAKE A CLOSER LOOK AT CATALYSTS.
ALL RIGHTY.
SO HERE WE HAVE A COUPLE OF REACTION ENERGY DIAGRAMS.
WE HAVE AN EXOTHERMIC REACTION AND LET'S SEE.
THEY ASK YOU TO LABEL THAT.
WELL, WE SEE EXOTHERMIC AND WE RECOGNIZE THAT RIGHT THERE AS
-DELTA H, RIGHT?
THE DIFFERENCE BETWEEN REACTANTS AND PRODUCTS.
WE HAVE THE SAME EXOTHERMIC REACTION.
NOTICE THAT IT HAS THE SAME DELTA H,
-DELTA H, THEY'RE THE SAME MAGNITUDE
AND THEN WE HAVE AN ENDOTHERMIC REACTION.
WELL, WE'LL JUST STAY WITH GREEN.
AN ENDOTHERMIC REACTION.
AND THEN HERE, NOW WE HAVE OUR +DELTA H. ALL RIGHT.
SO NOW THAT WE HAVE THAT PART FIGURED OUT,
LET'S LOOK AT THIS EFFECT OF THE CATALYST.
ALL RIGHT. SO HERE'S OUR ACTIVATION ENERGY
WITH NO CATALYST
AND THEN NOTICE WHAT HAPPENS TO THE ACTIVATION ENERGY
WHEN YOU DO HAVE A CATALYST, RIGHT?
SO WE'VE DONE THIS PART RIGHT DOWN HERE.
WE HAVE LABELED THE ACTIVATION ENERGY FOR B,
AND LET'S GO AHEAD
AND LABEL THE ACTIVATION ENERGY FOR C. ALL RIGHT.
SO NOW THAT WE'VE STUDIED OUR REACTION ENERGY DIAGRAMS,
LET'S THINK ABOUT WHAT ALL THIS MEANS, RIGHT?
SO A CATALYST IS A SUBSTANCE THAT INCREASES THE RATE
OF A CHEMICAL REACTION WITHOUT BEING CONSUMED IN THE REACTION.
SO WHAT CHANGES IN OUR REACTION ENERGY DIAGRAM?
HOW DOES THE CATALYST INCREASE THIS RATE?
WELL, IT SEEMS VERY OBVIOUS
NOW THAT WE'VE MADE THESE COMMENTS ON OUR--
ON OUR DIAGRAMS,
RIGHT, THAT IT-- THE CATALYST LOWERS, RIGHT,
DECREASES THE ACTIVATION ENERGY
AND THAT CREATES A FASTER REACTION RATE.
SO WHEN WE'RE TRYING TO LABEL THE REACTION ENERGY DIAGRAMS,
WE HAVE TWO THINGS TO CONSIDER, RIGHT?
EVERYTHING HINGES ON THE REACTANTS,
THE ENTHALPY IS THE DIFFERENCE BETWEEN REACTANTS AND PRODUCTS.
THE ACTIVATION ENERGY IS THE REACTANTS
TO THE TRANSITION STATE.
ALL RIGHT.
SO WE'VE GOT THOSE LABELED NOW. ALL RIGHT.
SO THE TRANSITION STATE THAT WE SYMBOLIZE TS,
THAT'S THE PARTICULAR ARRANGEMENT OF ATOMS
IN THE REACTANTS AT THE MAXIMUM ENERGY LEVEL, RIGHT?
SO REMEMBER THAT YOU WANT TO BE ABLE TO LABEL YOUR GRAPHS
SO YOU WANT NOTES TO YOURSELF, RIGHT?
THE ACTIVATION ENERGY IS THE MINIMUM ENERGY
TO REACH THE TRANSITION STATE.
AND SO REMEMBERING THAT WE GO FROM REACTANTS
TO TRANSITION STATE AND THEN TO WRAP THIS UP,
WHAT HAPPENS TO REACTANT MOLECULES
THAT HAVE LESS THAN THE ENERGY OF THE TRANSITION STATE, RIGHT?
SO THAT SAYING
THAT THE ENERGY IS LESS THAN THE ACTIVATION ENERGY, RIGHT?
SO THAT'S ANOTHER WAY TO PHRASE IT.
SO IF THE REACTANTS ARE COLLIDING AND THEIR ENERGY
IS BELOW THE ACTIVATION ENERGY, WHAT HAPPENS?
NOTHING, RIGHT?
THERE IS NO REACTION.
IF WE WANTED TO LOOK AT OUR GRAPH FOR EXAMPLE,
IF THE REACTANTS ONLY HAVE THIS MUCH ENERGY,
RIGHT, THEN WE COME TO HERE BUT THAT'S NOT ENOUGH.
THE REACTANTS HAVE TO GET ALL THE WAY UP TO HAVE ENOUGH ENERGY
TO GET ALL THE WAY TO THE TOP
OF THE TRANSITION STATE THEN THE REACTION WILL OCCUR.
AND SO AS WE VENTURE INTO BIOCHEMISTRY,
WE WILL LEARN THAT IN OUR BODY,
WE'RE GOING TO USE ENZYMES AS OUR BIOCHEMICAL CATALYSTS.
ALL RIGHT.
SO THIS CONCLUDES THE REACTION RATES KINETICS VIDEO TUTORIAL.
TAKE SOME TIME NOW TO WORK A FEW HOMEWORK PROBLEMS
TO REINFORCE YOUR UNDERSTANDING.