Chapter 1 - Rate of Chemical Reactions Flashcards
What is the Rate of Reaction?
The change in concentration of a reactant or product over a period of time (usually one second) …or a measure of how quickly reactants produce products.
**RATE OF REACTION USUALLY DECREASES OVERTIME
The equation to find the rate of reaction
Change in concentration
Rate of reaction = —————————————–
Time
How can the rate of a reaction be measured?
Experimentally the rate of reaction can be determined by measuring, either
DIRECTLY or INDIRECTLY, the formation of the products or the depletion of reactants OVER TIME.
What are the FACTORS THAT CAN BE MEASURED TO DETERMINE THE RATE OF A REACTION?
- Mass lost by reagent
- Mass gained by product
- Volume of gas
- Pressure of gas
- Colour intensity
- Solution Concentration
- pH
Different reactions may lend themselves to specific experimental methods of determining the reaction rate.
What is the collision theory?
A theoretical model that accounts for the rates of chemical reactions in terms of collisions between particles occurring during a reaction.
- A chemical reaction is the result of a successful collision between particles.
In order for a collision to be successful, the reactant particles must collide with:
- CORRECT ORIENTATION
- SUFFICIENT ENERGY
If EITHER CRITERION is NOT MET, the COLLISION will NOT BE SUCCESSFUL and NO CHEMICAL CHANGE will occur.
Explain the correct orientation, and why it is important?
CORRECT ORIENTATION: Molecules need to collide at the correct orientation which ALLOWS FOR THE BREAKING OF EXISTING CHEMICAL BONDS and the FORMATION OF NEW CHEMICAL BONDS
The orientation of colliding particles is the RESULT OF THIER RANDOM MOTION
NOT SOMETHING THAT CAN BE EASILY MODIFIED TO INCREASE THE RATE OF REACTION
Large or complex sites where the reactive sites represent only a small part of the whole molecule only have a very small number of collisions with the appropriate orientation: resulting in a very slow reaction rate.
Similarly, molecules with extensive structures where the reactive are obscured from colliding with other reactant particles don’t react any appreciable extent.
Explain SUFFICIENT ENERGY and why it is important?
SUFFICIENT ENERGY: When 2 reactant particles collide, they still need to have a certain amount of KINETIC ENERGY for a successful collision and generations of products.
The energy requirement of the bond breaking (and formation) process.
- - Particles have a range of kinetic energies as a result of the particles moving at different velocities. - - However, at any given temperature, the energies possessed by the particles moving at different velocities. - The energy required for the particles to collide successfully is more easily modified.
What is Kinetic energy? and the formula?
Kinetic energy is the energy that a particle or body has due to its motion.
KE = ½mv^2
What is Activation energy? and its notation.
The minimum amount of energy required to break the existing chemical bonds, allowing the collisions to be successful
Notation - Ea
What is the MAXWELL-BOLTZMANN DISTRIBUTION CURVE or KINETIC ENERGY DISTRIBUTION DIAGRAM?
Draw an example and explain what it shows:
A probability distribution function that shows the range of kinetic energies possessed by the particles in a substance at a specific temperature.
It shows - Distribution of energies of particles in a sample at a particular temperature
- They represent how a specific variable (e.g., KINETIC ENERGY) is DISTRIBUTED AMONG POPULATION OF PARTICLES.
- Curves do not show the relationship between 2 simple variables
What is an energy profile diagram?
a diagram that shows the energy changes during the course of a reaction.
What is an exothermic reaction?
An exothermic reaction releases energy to the surroundings:
= ΔH is negative
What is an endothermic reaction?
A reaction that absorbs energy from the surroundings:
= ΔH is positive
What is the transition state? and what does it mean?
An arrangement of atoms in a reaction that occurs when sufficient energy is absorbed for the activation energy to be reached.
- It represents the stage of maximum potential energy in a reaction.
- Bond breaking and bond-forming are both occurring at this stage, and the arrangement of atoms is unstable.
Draw energy profile diagram drawings of exothermic and endothermic reactions
compare and learn how to calculate them
What are the Factors affecting the Rates of Reaction?
- NATURE OF REACTANTS IN THEIR BOND BREAKING CAPACITY (eg. Covalent molecular is covalent network)
- CONCENTRATION OF REACTANTS
- SURFACE AREA: SUB-DIVISION OF REACTANTS (large chunk vs. Powdered/crushed)
- TEMPERATURE
- PRESENCE OF A CATALYSTS
- GAS PRESSURE
