Chem Rates of Reaction

Rate of Reaction

Change in concentration of a reactant or product per unit of time

Collision Theory

Particles must collide

Must collide with sufficient energy

Must collide with correct orientation

Factors Affecting Rate of Reaction

Concentration of reactants

Pressure of any gaseous reactants

Temperature

Surface area of solid reactants

Presence of catalyst

Concentration

More particles present

Increased frequency of collisions

Increased number of successful collisions

Gas Pressure

Increases concentration of gas molecules

Causes more frequent collisions

Increases number of successful collisions

Surface Area

Increases number of particles present at solids surface

Increases frequency of collisions & successful collisions

Temperature

Measures the average kinetic energy of the particles in a substance

As temperature increases, the speed of particles increases

Causes more collisions and successful ones

Catalysts

Provides alternative chemical pathway with a lower activation energy

Increases proportion of reactant particles with energies higher than activation energy

Aren't consumed during reaction

Nature of Reactants

Ionic in solution = faster rate

Covalent in solution = slower rate

Particle Theory of Matter

Matter is made of atoms

Particles are in constant motion

Particles are held together with strong electrostatic forces

Spaces between particles are very large

Heat v Temp

Heat = energy transferred from one object to another with different temperatures

Temperature = measure of average kinetic energy of particles

Solids

Strong electrostatic forces

Densely packed

Particles constantly vibrate

Have vibrational energy only

Liquids

Weaker electrostatic forces than in solids

Can move within walls of container and bumping into other particles (translational energy)

Is able to be poured and spread to fit container

Have vibrational energy & translational energy

Gases

Very weak forces

Can move and bump into container sides & against other particles

Rotate and vibrate at the same time

Have rotational, vibrational and translational energy

Energies (Potential)

Solids = small spaces between particles = low potential energy

Liquids = large spacing between particles = higher potential energy

Gases = very large spacing between particles = even larger potential energy

Energies (Kinetic)

All particles have kinetic energy as they are always moving

Heating a substance increase kinetic energy as particles have faster velocities

Kinetic energy = 1/2mv²

Kinetic Theory of Gases (Ideal Gases)

Tiny particles

Always moving in rapid, straight line until collision

Particles have mass but no volume

Average kinetic energy of particles increases as temp increases

Diffusion

Spreading out of gas

Particles move in rapid, straight line motion until collision

Can keep moving as no attractive forces

Compression

Volume of gas particles is negligible compared to volume of container occupied by gas

Gases can be compressed into small spaces

Boyles' Law

Temp is constant

Decrease in volume causes particles to hit container more frequently, so pressure increases

Charles' Law

Pressure is constant

Increase in temp means that volume of container must increase

Gay-Lussac's Law

Volume is constant

Decrease in temp means less collisions with side of container, decreasing pressure

Avogadro's Law

Gases at same temp & pressure contain the same number of particles

Volume occupied by a gas is proportional to the amount of moles of gas present

Units of Pressure

1 atmospheric pressure = 101.3 kilopascals

Kelvin Scale

K = C + 273