The Rate And Extent Of Chemical Change Flashcards
How is rate of reaction calculated?
Rate of reaction = amount (e.g. grams) of reactant used or product formed / time
What are the various units for rate of reaction?
Mass/time, volume/time, moles/time (can include g/s or cm3 or mol/s)
What are the common ways of measuring rate of reaction?
- loss in mass of reactants
- volume of gas produced
- time for a solution to become opaque
Describe measuring the rate of reaction by monitoring mass loss
Place the reaction flask on a balance. In these reactions a gas is given off, so record the decrease in mass in time intervals -> plot a graph of mass vs time
Describe measuring the rate of reaction by monitoring the volume of a gas
Connect a gas syringe to a reaction flask and measure the volume of a gas formed in time intervals -> plot a graph of volume vs time
Describe measuring the rate of reaction by monitoring the disappearance of a cross
Take a piece a paper and mark a cross (X) on it. Put the reaction flask on this cross. Mix the reagents, and measure how long it takes for a cloudy mixture to conceal a cross
How do you find a rate of reaction at some time from a graph of the amount of reactant vs time?
- pick a point corresponding to the time and find the tangent to the curve at this point
- the tangent is the gradient of this graph - it tells you how fast the reaction proceeds at this point
- the steeper the tangent line, the faster the rate
- gradient of tangent can be expressed in change in y values over change in x values
What five factors affect the rate of a chemical reaction?
- concentration
- pressure of gases
- surface area
- temperature
- catalysts
What is activation energy?
the minimum quantity of energy which the reacting species must possess in order to undergo a specified reaction. It is also called sufficient energy
How does concentration/pressure affect the chemical reaction?
More particles per unit of volume ~ collision will be more frequent and will increase the rate of reaction
How does surface area affect chemical reactions?
The smaller the surface area ~ more frequent the collisions are and will increase the rate of reaction
How does temperature affect the chemical reaction?
As the temperature increase, the particle gain more energy ~ move faster, collide more frequently and will increase the rate of reaction (up 20 degrees can double the reactions)
How can catalyst affect the chemical reaction?
Higher proportions of catalysts ~ more successful collisions and will increase the rate of reaction
What is a catalyst?
Substance that can be used to speed up a reaction without being used up in the reaction themselves
What is the collision theory?
Chemical reaction can occur only when the reacting particles collide with each other with sufficient energy (more than or equal to activation energy)
What is an enzyme?
Molecule that acts as a catalyst in a biological system
What is a reversible reaction?
A reversible reaction occurs when the product of a reaction can react backwards to produce the originals reactants
When is dynamic equilibrium reached?
In a closed system, when the forward and reverse reactions occur at the same rate and the concentrations of reactants and products remain constant
Describe Le Chatelier’s Principle
If a system is at equilibrium and a change is made to any of the conditions, then the system responds to counteract change and restore the equilibrium
Describe the effect of change the concentration of reactant and product on the position of the equilibrium
If the concentration of one of the reactant or products is changed, the system is no longer at equilibrium and the concentrations of all the substances will change until equilibrium us reached again. If concentration of a reactant is increased more products will be formed until equilibrium is reached again. If the concentration of a product is decreased, more reactants will react until equilibrium is reached again
Describe the effect of changing temperature on the position of the equilibrium
If the temperature of a system at equilibrium is increased
- the relative amount of products at equilibrium increases for an endothermic reaction
- the relative amount of products at equilibrium decreases for an exothermic reaction
Describe the effect of changing pressure (of gases) on the position of the equilibrium
An increase in pressure causes the equilibrium positions to shift towards the side with the smaller number of molecules as shown by the symbol equation for that reaction. A decrease in pressure causes the equilibrium position shift towards the side with a larger numbers of molecules as shown by the symbol equation for that reaction. Pressure has no effect on the reactions where the numbers of gas molecules are equal on both sides of the equation
Describe the effect of a catalyst on the position of the equilibrium
No effect -> it just speeds up both forward and backward reactions equally i.e. equilibrium is achieved faster
What is concentration?
A measurement of how much solute exists within a certain volume of solvent
What is gas pressure?
The force that the gas exerts on the walls of its container
What is finding the rate?
Amount of reactant used or product formed
How do you find the mean rate from reactants?
Reactant used / time
How do find the mean rate of products?
Product formed / time
What the the rate from a graph?
The steeper the gradient is, the faster the rate
What is the mean rate?
Average rate over a time range
What is a specific rate?
Reaction rate at a specific time
How do you calculate the gradient?
Change in y / change in x
