The Rate and Extent of Chemical Change Flashcards
How do we measure the rate of a reaction?
- Measuring how fast the reactants are used up
or - Measuring how fast the products are forms
Rate of Reaction Equation
Quantity of Reactants used up (g or cm3) /Time Taken (s)
Rate of Reaction Equation 2
Quantity of Products Formed (g or cm3) /Time Taken (s)
Mass of reactant on a graph
- At first decreases rapidly
- Slows as reaction progresses (reactant gets used up less quickly)
- Mass of reactant is 0
Volume of product on a graph
- Starts at 0 (no products yet)
- Quickly increases as product is formed
- Graph becomes less steep
- Eventually plateau’s (levels off) when a reactant is used up
What affects the rate of a reaction?
- Temperature
- Surface Area
- Absence/Presence of catalysts
- Concentration/Pressure
Collision Theory
For particles to react, they have to collide with each other with a sufficient amount of energy
What factors affect collision theory?
- Amount of energy the particles have (more energy means more energy transfer during collisions)
- Frequency of collisions (more frequent collisions mean more successful ones)
How does temperature increase rate of reaction?
- Temp. increase means particles gain more energy
- Particles move faster
- More frequent collisions
- Collide with more energy
- More likely to exceed activation energy
- More successful collisions
How does concentration/pressure increase rate of reaction
- Increase in concentration/pressure means increase in particles (per unit of volume)
- More frequent collisions
- More successful collisions
- Increase in reaction rate
How does surface area increase rate of reaction?
- Increase in surface area means higher SA:V ratio
- More frequent collisions
- Higher rate of successful collisions
Catalyst
Substances that speed up rate of reaction without being used up (aren’t included in the reaction equation)
How do catalysts increase rate of reaction?
- Lower activation energy by providing alternative reaction pathways
What is a Reversible Reaction?
A chemical reaction that can happen in both directions
What is Equilibrium?
When the concentrations of the forward and backward reactions of a reversible reaction remain constant
Where does the equilibrium lie when there are more products?
To the right of the equation
Where does the equilibrium lie when there are more reactants?
To the left of the equation
What conditions impact the position of equilibrium?
-Temperature
-Pressure
-Concentration
When can equilibrium be reached?
When the reversible reaction is done in a closed system
What is Le Chatelier’s Principle?
When changing the conditions of a reversible reaction, the position of equilibrium will change to counteract the change
What happens when the temperature of a reversible reaction is decreased?
The position of equilibrium moves the side of the reaction that is exothermic. Exothermic reactions create temperature increase and that counteracts the decrease
What happens when the temperature of a reversible reaction is increased
The position of equilibrium moves the side of the reaction that is endothermic. Endothermic reactions create temperature decrease and that counteracts the increase
What happens when the pressure of a reversible reaction is increased?
The position of equilibrium moves to the side of the equation with the least molecules
What happens when the pressure of a reversible reaction is decreased?
The position of equilibrium moves to the side of the equation with the most particles
What happens when the concentration of a reversible reaction is increased?
The position of the equilibrium moves to the other side of the equation and produces more product/reactant (depends on what side the equilibrium was initially on)
What happens when the concentration of a reversible reaction is decreased?
The position of the equilibrium moves to the other side of the equation and produces less product/reactant (depends on what side the equilibrium was initially on)
Pressure only impact substances in what state?
Gaseous
