2.1 Rates of Reactions Flashcards
(26 cards)
Rate of chemical reaction (RoR)
How fast or slow successful collisions occur per unit time.
Measured through concentration of reactants consumed and products formed with respect to time elapsed.
Law of Conservation of Energy
Energy cannot be created or destroyed.
Law of Conservation of Mass
The total/net mass of a system is conserved during a chemical reaction.
Collision Theory
For a successful collision to occur between reacting particles, it must have:
1) Sufficient energy
2) Correct orientation
Activation energy (Ea)
Minimum amount of energy required for a successful collision to occur.
2 main factors controlling RoR
1) Frequency of collisions per unit time
2) Proportion of collisions reaching or exceeding Ea, therefore being successful
Average RoR
RoR over a specified time interval; slope of line over this period.
Instantaneous RoR
RoR at a particular point in time; slope of tangent line drawn at this point.
Useful for determining highest rate of production.
Graphically interpreting RoR
Gradient of a quantity-time graph
Gradient of a graph
(change in y)/(change in x)
Steep gradient
Rapid RoR
Shallow gradient
Slower RoR
Zero gradient
Non-reversible: reaction stopped occurring
or
Reversible: reaction reached a state of chemical equilibrium
Impact of increasing concentration of reactants on RoR
More reacting particles present in same amount of volume.
Frequency of collisions increased.
Therefore, increased RoR.
2 ways of increasing pressure
1) Decreasing volume of system
2) Introducing more particles into given volume
Impact of increasing pressure of gaseous reactants on RoR
Increased concentration of gaseous reacting particles.
Frequency of collisions increased.
Therefore, increased RoR.
Pressure and state of matter
Only affects gas-phase reactions.
Surface area and state of matter.
Only affects solid-phase reactions.
1 way of increasing surface area
1) Division into smaller particles
Impact of increasing pressure of solid reactants on RoR
More reactant particles exposed and more area for reactant particles to collide with.
Frequency of collisions increased.
Therefore, increased RoR.
Impact of increasing temperature of system on RoR
Increased average kinetic energy, as reacting particles have more thermal energy.
So, particles move faster, and frequency of collisions increased.
Also, larger proportion of collisions reach or exceed Ea, so there are a larger number of successful collisions.
Therefore, increased RoR.
Impact of presence of a positive catalyst on RoR
Catalyst provides alternative pathway for reaction to proceed with lower Ea.
Larger proportion of collisions reach or exceed Ea, so there are a larger number of successful collisions.
Therefore, increased RoR.
Enthalpy
H
Energy content of a system at constant temperature and pressure.
Energy profile diagram
Represents conversion of reactants into products, and their relative energies.
x-axis: reaction pathway
y-axis: total thermal energy of system (H)
Ea is line between highest and lowest energies.
ΔH is line between highest energy and reactants’ energy.
