Reaction Rate Notes CP Chemistry Chapter 16
Dec 30, 2015
Reaction Rate Notes
CP Chemistry
Chapter 16
Reaction Rates
Speed at which chemical reactions occur can vary greatlySpace rocket = fastConcrete hardening = slowFossil fuels created = very, very slow
Reaction Rate DefinedDefinition: the change in concentration of a reactant or product per unit of timeOR: the amount of change in a reactant or
product measured over timeExamples of rates:Sprinter: meters/secondCar: miles/hourReaction rate: concentration/time
(Molarity/second, moles/L/s)
Reaction Rate Equation
Equation:
time must be measured in
seconds!
Reaction Rate Example Problem
Determine the rate of reaction if a 2 M concentration of NaCl increases to an 8 M concentration after 10 seconds of the reaction has passed.
Collision TheoryTheory = atoms, ions, and molecules MUST collide
in order to reactNOTE: not all collisions of particles produce
reactions – must meet three requirements
Requirements for a Reaction to Occur
1. Particles must COLLIDE
2. Particles must have CORRECT ORIENTATION
3. Particles must have SUFFICIENT ENERGY (ACTIVATION ENERGY)
Correct OrientationAtoms, molecules, or ions without the proper
orientation will NOT react If proper orientation occurs – forms activated
complex (transition state)Active complex = temporary, unstable arrangement
of atoms that may form reactants or products
In order for something to be produced, what must the molecules do?
Crash Course
What are the two criteria that must be met when particles collide?
For example, how is water produced? What must collide?
1. 2.
Activation Energy
Definition: the minimum amount of energy required by the reacting particles in order to form the activated complex and lead to a reaction
Activation energy (Ea) determines if the activated complex will form reactants or products
Products or Reactants?If enough energy is available to overcome activation energy, products will form
If NOT enough energy is available to overcome activation energy, reactants will form
Like trying to push a boulder over a hill – it takes energy to get to top, but at the top it rolls easily down other side
Mini Lab Activity – I’m Feeling Dizzy
To see how important energy is to controlling a reaction, you are going to design an experiment using marbles and a petri dish.
1. You must find the relationship between temperature, the frequency of collision, and the energy needed to cause a change from reactants to products.
Results:
What you have just modeled from the activity was called the activation energy, Ea, of a reaction.What is activation energy (Ea)? What can we compare activation energy to?
What is an activated complex and where does it form?
Energy DiagramsExothermic Reactions
energy is releasedproducts will have lower
energy than reactants
Endothermic Reactionsenergy is absorbed reactants will have lower
energy than products
What is the difference between the diagrams? Label them as endothermic and exothermic. How does Ea affect a reaction?
Factors Affecting Reaction Rate
Five factors can influence how fast a reaction will occur:
1. Nature of the reactants
2. Concentration
3. Surface Area
4. Temperature
5. Catalysts (Inhibitors)
Nature of Reactants
Depending on their positions in the periodic table, some elements release their electrons easier than others
Example: Elements in families 1A & 2A are more reactive than those in 3A & 4A
Also, as move down a family, elements may react faster or slower – elements in families 1A & 2A react faster as you move down the family
Concentration
More particles more collisions more activated complexes more product formed
Lower concentration = lower reaction rateHigher concentration = higher reaction rate
Surface Area Increasing the surface area of the reactants increases the
sites available for collisions more collisions increased reaction rate
Less surface area = lower reaction rate Higher surface area = higher reaction rate
Temperature
Increasing the temperature of the reactants causes them to move faster – have more kinetic energycauses more collisionshave more energy – enough to overcome
activation energyLower temperature = lower reaction rateHigher temperature = higher reaction rate
Catalysts
Definition: a substance that increases the rate of a chemical reaction by lowering the activation energy but is not itself consumed in the reactionNOT a product or a reactant
InhibitorsDefinition: type of catalyst that slows down the reaction rate of a chemical reaction or prevents a reaction from occurring
Factors That Affect Reaction Rates Name the five factors that affect the reaction rate:
1. What happens to group 1A elements when they are placed in water?
2. How does concentration affect the rate of a reaction?
3. What is surface area and how does it affect reaction rate?
4. Popping the Top activity – how does temperature affect the rate of reaction?
5. Mini Lab Activity – Jeanie in a Bottle – How does a catalyst affect the rate of a reaction?
Factors That Affect Reaction Rates
This graph represents the energy of particles at two different temperatures. T1 is at a lower temperature than T2. A. What do you notice about the height of the hills? Which one is higher? B. Notice that curve T2 is shifted relative to T1. What happened to the number of particles as the temperature increased relative to the activation energy? C. If you wanted to increase the rate of reaction, how would you do it according to the chart? D. Based on what you wrote, why would your guess work?
What is the difference between a homogeneous catalyst and a heterogeneous catalyst?
homogeneous catalyst Example
heterogeneous catalyst Example
Look at the chart below. Can you figure out how a catalyst works?Answer:
What can we use to slow down the rate of reaction? ________________
Test Tube 1 Test Tube 2 Test Tube 3 Test Tube 4
10 mL HCl0 mL waterTotal = 10 ml
6 mL HCl4 mL waterTotal = 10ml
3 mL HCl7 mL water Total = 10ml
1 mL HCl9 mL waterTotal = 10ml
Before = afterM1V1=M2V2
3 (10) = x (10)X = 3 M
Before = afterM1V1=M2V2
3 (6) = x (10)X= 1.8 M
Before = afterM1V1=M2V2
X = ?
Before = afterM1V1=M2V2
X= ?
1.Add water to test tubes 2-4
2.Time how long Mg reacts and record data
3.Clean test tubes and return to front table