What Determines Rate of Reactions

Effective Collision

• Kinetic Particle Theory Main Note
• Particles are in constant random motion → will thus constantly collide with each other.
• Some collisions successful in breaking existing bonds and/or forming new bonds → resulting in chemical reaction

Definition

When a chemical reaction occurs between particles, collision is said to be an effective collision #ChemistryDefinitions

Definition

Activation Energy is the minimum amount of energy that reacting particles must possess in order for chemical reaction to proceed. #ChemistryDefinitions

Important

For effective collision to occur → reactant particles must collide with energy that is greater than or equal to the activation energy.

• once this condition is met → there will be effective collisions → between the reacting particles → resulting in product particles being formed
• (these effective collisions where existing bonds in reacting particles are broken and new bond are formed in the products)

Important

NEED TO SAY “FREQUENCY OF EFFECTIVE COLLISION INCREASES / DECREASES” DO NOT EVER SAY “RATE”

Note

R.S between frequency of effective collisions and rate of reaction

• higher frequency of effective collisions between reacting particles per unit time → the greater the amount of products formed per unit time → thus the rate of reaction will be faster.

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Factors Affecting ROR

• any factor (variable) → that affects frequency of effective collisions between reacting particles → will affect speed of chemical reaction.

5 Main Factors

1. Concentration of Reactant(s) in Aqueous State
2. Pressure at which Reaction Occurs
3. Particle Size of Reactant(s) in Solid State
4. Temperature at which Reaction Occurs
5. Presence of Catalyst

Other Possible Factors + Links

• Basicity of acids (link to concentration) Basicity of Acids
• Strength of acids (link to concentration) Strong and Weak Acids
• Reactivity of metals Reactivity Series Main Note
• Thermal stability of metal carbonates…etc Thermal Decomposition of Metal Carbonates
• More initial mass of reagent added*
• Layer of insoluble salt formed
• Layer of aluminium oxide*

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Sample

Magnesium metal reacts faster with 1.0mol/$d{m}^3$ of sulfuric acid compared to 1.0mol/$d{m}^3$ of hydrochloric acid i) write chemical equations to illustrate the reaction between magnesium and the 2 acids ii) explain why magnesium metal react faster with sulfuric acid than with hydrochloric acid

• Skip chemical equation part.

• HCl → monobasic acid → $1H^{+}$ ion for every molecule upon ionization in water.

• Sulfuric acid → dibasic acid → $2H^{+}$ ions when each molecule of acid ionizes in water.

• higher concentration of $H^{+}$ ions in 1mol/dm3 Sulfuric acid compared to 1mol/dm3 Hydrochloric acid, by 2 times. Thus Sulfuric acid is a stronger acid than HCl.

• Number of $H^{+}$ ions per unit volume is higher → thus there are more collisions between Mg and H+ ions, which causes increase in frequency of effective collision between these particles.

• Thus faster reaction with sulfuric acid compared to hydrochloric acid

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