rates of reaction and equilibrium
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Rates of Reaction and Equilibrium
•Rates of reaction = kinetics
•Equilibrium = balance
To react, atoms must get together: • Called the collision theory:
• Students act a chemical reaction
• 1.
• 2.
• 3.
To react, atoms must: 1. Get together (collide)2. Get together in the right way (orientation)
Collide with the “correct” side of a moleculeNO₂ + CO ↦ NO + CO₂
Carbon must hit the O side of NO₂ to get one of the O from the NO.
3. Get together with enough energy (force) so that the electrons can be shared/transferred
1. Activation energy (low or high)
Rate of chemical reaction:
Reaction Rate
= Collision frequency
factor
X Collision orientation
factor
X Collision Energy Factor
Reaction rate of a chemical reaction: measured by change in concentration per unit time
REACTION RATES: KINETICS• Rate that reactants turn into products
• Measured by change in concentration (of reactants or products)
5 FACTORS AFFECTING REACTION RATES3 factors relate to energy
2 factors relate to the particles
Review collision theory• Chemical reactions happen when atoms and compounds collide with each other
• Collide with sufficient force to break bonds
• Collide in the right position (orientation)
Factors affecting collision theory - Why?
Energy • Temperature
• Agitation
• Catalysts
Characteristics
• Concentration
• Surface area
Energy & kinetics (rate)• 1. temperature: increases temp INCREASES reaction rates
Why? *particles move faster and collide with greater intensity
2. agitation: increases reaction rate Why? *increases likelihood of particles being exposed to one another; increase in collisions
examples: shaking, stirring
Energy & kinetics3. catalysts: substance that increases the reaction rate without being used up in the reaction. Why? * lowers the ACTIVATION energy; sort of “invites” reacting particles together so they will react
Solutions & kinetic• concentration: increasing concentration of reactants increases rate
Why? *increasing # particles increases chance of collision resulting in a reaction
• 2. surface area: increasing will cause reaction rate to increase
Why? *greater exposure of reacting particles to each other
examples: pulverizing, crushing, chopping up, etc Example: Logs vs. twigs
Collision Theory • Speed up the rate of reaction • https://www.youtube.com/watch?v=OttRV5ykP7A
CHEMICAL EQUILIBRIUM = BALANCE
Chemical EquilibriumKey Terms• Reversible reactions • Balance • Impacted by concentration, temperature and pressure
• Closed system (no new reactants added, no product is removed)
• Equilibrium constant • Keq = [products] [reactants]
Chemical Reaction Equilibrium
•Reversible reactions: ↔⇄
• Explain what a reversible reaction will do to products and reactants
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Chemical Reaction Equilibrium
•Reversible reactions: ↔⇄
• Often happens naturally• Products can be turned back to reactants• In other words: Products recombine to form the original substances .
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Reversible reactions and Equilibrium• Equilibrium = balance between the amount of
reactants and products in a reversible reaction
Needs a closed system: no additional reactants added and no products are taken away or escape as a gas)
Dynamic equilibrium Forward and backward reactions taking place at the same rate
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Chemical Equilibrium
Chemical Equilibrium = Balance
Achieving equilibrium: After a period of time, the concentrations of reactants and products will stabilize
Time from start of reaction
ReactantConcentration
Product Concentration
0 20 0
10 12 820 8 12
30 6 14
40 6 14
50 6 14
Le Chatelier Principle• If you change the conditions, the position of the
equilibrium will shift to oppose the change.
• Apply stress
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Upsetting the equilibrium to make more product Upsetting the equilibrium = shifting the equilibrium • Change temperature
If an endothermic reaction -absorb or release heat? -example of types of reaction?
CaCO₃ + heat ⇄ CaO + CO₂Add more heat (raise the temperature) to make more
product
If an exothermic reaction – reduce the amount heat (lower the temperature) to make more product
Reaction will try to replace the heat that was taken away
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Upsetting the equilibrium to make more product
• Change the pressure • Important when gases react• Many reactions will have greater volume on one side (more product
or more reactant)
If we increase the pressure – The reaction will “favor” the reaction side with less volume
If we lower the pressure – The reaction will “favor” the reaction side with more volume
N₂ + 3 H₂ ⇄ 2NH₃
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Haber Process • TED Ed Lessons
• https://ed.ted.com/lessons/the-chemical-reaction-that-feeds-the-world-daniel-d-dulek
• New concept: equilibrium
Le Chatelier Principle• If you change the conditions, the position of the equilibrium will shift to oppose the change.
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Stresses disrupt the balance
Equilibrium constant
•aA + bB ⇆ cC + dD•Keq = [C] [D] [A] [B] • Example: N₂ + 3 H₂ ⇄ 2NH₃ • Keq = [NH₃]² [N₂] [H₂]³
Add coefficients at exponents
Will use equilibrium constant when determining pH and pOH
Issues- Chemical reactions Good & Evil • Haber received much criticism for his involvement in the d
evelopment of chemical weapons in pre-World War II Germany, both from contemporaries and from modern-day scientists.
• The research results show the ambivalence of his scientific activity: on the one hand, development of ammonia synthesis for the manufacture of explosives and of a technical process for the industrial manufacture and use of poison gas in warfare; but on the other hand, development of an industrial process without which the food supply for today's world population would be greatly diminished
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Review: Energy in chemical reactions
Exothermic chemical reaction
Review: Energy in chemical reactions
Endothermic chemical reaction
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