Rates of Reactions (2) Flashcards
Topic 2
What is a concentration vs time graph?
Due to differential calculus, the slope is the rate at which concentration changes over time (i.e. the reaction rate)
This is measured in the unit of ๐๐๐๐ฟ^(โ1) ๐ ^(โ1)
The time scale may vary depending on the length of the reaction
Other variables (pH, volume, pressure, colour change, light) can be used to track reaction rate
What does a steep slope of a rate of reaction graph mean?
Steep slope (large slope) = rapid rate of reaction
What does a shallow slope of a rate of reaction graph mean?
Shallow slope (small slope) = slow rate of reaction
What does no slope of a rate of reaction graph mean?
Zero slope = no reaction occurring OR reaction has reached equilibria
What is an exothermic reaction?
Energy is absorbed and temperature decreases.
What is an endothermic reaction?
Energy is released and temperature increases.
What is collision theory?
- Successful collisions result in product formation:
The kinetic energy of the colliding particles exceeds the activation energy for the reaction - Unsuccessful collisions result in no products formed and no chemical change:
The kinetic energy of the colliding particles does not exceed the activation energy for the reaction leading to the particles bouncing of one another
What criteria must be met for a reaction to occur?
For a reaction to occur, the following three criteria must ALL be met:
- The reactant particles (molecules, atoms or ions) must collide
- The colliding particles must have energy equal to or more than the activation energy
- The reactant particles must collide in the correct orientation for a reaction to occur.
How can you increase reaction rate?
Based on collision theory, to increase a reactionโs rate we would have to ensure that particles:
Frequently collide
Collide in the correct orientation
Collide with energy equal to or greater than a reactions activation energy
What factors could we use to alter these conditions?
Temperature
Concentration
Pressure
Surface area
Catalysis
Enzymes
How does temperature effect reaction rate?
The higher the temperature, the particles move faster due to the greater amount of kinetic energy.
This increases the chances of a molecule colliding with energy equal to or greater than the activation energy.
How does concentration effect reaction rate?
The higher the concentration, the more particles per unit volume. The closer particles are and more likely they are to collide. Increasing the concentration of reactants, increases the frequency of successful collisions
How does pressure effect reaction rate?
The pressure of a gas can be increased by decreasing the volume, allowing particles to collide more frequently. Decreasing the container size, increases the gas pressure, which increases the probability of successful collisions and indirectly, the frequency of successful collisions.
What is the role of a catalyst?
Catalysts increases the rate of reaction by providing alternate energy pathways that lower activation energy
Catalysts are not consumed during the reaction and remain unchanged at the completion of the reaction โ require only small amounts
Homogenous catalysts โ same state (solid, liquid gas)
Heterogeneous catalysts โ different state
What is equilibrium?
When the rate of a forward reaction and backward reactions are equal, the systems is said to be at equilibrium
Equilibrium is a dynamic (moving) process. The reaction has not stopped, it is just happening equally as fast in both directions
At equilibrium there is no change in observed or measured proprieties such as colour, temp, pH, pressure or concentration
What conditions need to be met for equilibrium to occur?
A system (i.e. a reaction) can only reach Equilibrium if:
- It is closed (reactants, product cannot be lost or gained to/from surroundings.
- It is at a constant pressure.
If these conditions are not met, the forward (right) or the backward (left) reaction will be favored.
