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