C8- the rate and extent of chemical change 💥 Flashcards
What is the rate of a chemical reaction ?
- the rate of a chemical reaction, is the speed at which a chemical reaction takes place
How can the mean rate of reaction be calculated ?
Hint: quantity/time
- the mean rate of reaction can be calculated, by using equation=
- quantity of product formed ➗ time taken
In a reactant —> product graph, what does the slope of the line tell us ?
- if the quantity of product against time is plotted, the slope of the line gives us an idea of the rate of reaction.
- this is because, the sleeper the slope, the faster the reaction
In the reactant —> product graph, for the quantity of product formed against time, why does the graph get less steep ?
- ; the slope of the line will gradually become less steep- telling is rate of the reaction is decreasing [the reaction is slowing down.]
- this is because, a lot of the reactant molecules have already reacted, and turned into product- therefore, fewer reactant molecules are available to react.
In the reactant —> product graph, why is the slope of the line now zero, and the line is flat. [at the end]?
Hint: all the reactant molecules…
- at the end, the slope of the line is now zero, and the line is flat.
- this is because, at this point the reaction has stopped, since all of the reactant molecules have already reacted.
What are the units for the quantity of product formed ?
Hint: not a compound unit
- the quantity of product formed is typically in grams
- ; if our product is a gas, the quantity is then measured in cm^3
What does the reactant —> product graph, look like ?
- the rate is initially fast; the reaction then slows down and the reaction finally stops
Define the term ‘collision theory ?’
Hint: how chemical reactions…
- collision theory, is a scientific explanation of how chemical reactions occur.
- ; collision theory also explains how various factors, can affect the rates of reactions
Explain the concept of collision theory
Hint: reacting particles…
- collision theory states that: chemical reactions can only occur, when the reacting particles collide with each other.
- This is because, the collisions must have sufficient energy
- ; collision theory also states, the rate of a chemical reaction, is determined by the frequency of fruitful collisions [successful]
What do collision theory state, as the reason for a reaction between reactants ?
Hint: collisions
- collision theory states that the reaction between reactants, is due to: the collisions of the reactants particles, and the energy they have when they collide
According to collision theory, why don’t all collisions lead to a reaction ?
Hint: minimum energy
- not all collisions lead to a reaction because, they have a certain minimum energy known as the activation energy.
- Fill in the gaps: Any change in __________ that increase: the number of collisions and the ______ of the particles, will increase the ____ of reaction.
- Any change in conditions that increase: the number of collisions, and the number of the particles, will increase the rate of reaction.
Why are the five conditions [factors], that the rate of [chemical] reactions depend on ? [5]
Hint: catalyst
- temperature
- the concentration of liquids, and pressure of gases.
- the surface area of solid reactants
- and, the presence or absence of a catalyst
What does frequency mean ?
Hint: number
- frequency, is the number of successful collisions, per second
Explain the effect of surface area, on rate of reaction
Hint: collision theory
- collision theory states, that the reaction between reactants is due to: the collisions of the particles of the reactants, and the energy they have when they collide is needed
- so increasing the surface area, exposes more solid particles to the other reactant
- this then increases the frequency of successful collisions [of the reactants’ particles]- and therefore, the rate of reaction increases.
- This is because, if surface area increases—> more particles are available to react——> more successful collisions——> and the rate of reaction increases.
How is surface area: volume ratio affect rate of reaction
Hint: smaller size blocks of solid rectant
- smaller sized blocks of solid reactant, have a greater surface area: volume ratio than larger blocks
- meaning that smaller sidled blocks of solid reactant, have more particles on the surface- meaning there are more collisions per second [per unit time]
- and, this increases rate of reaction
How can the surface area of a solid reactant be increased ?
- the surface area of a solid reactant can be increased, by:
- breaking it up into very small pieces, and decreasing the particle size
State the units for rate of reaction ?
Hint:
- the units for rate of reaction, are: g/s , cm^3/s and mol/s
Explain how there can be different units, for measuring rate of reaction
- there can be different units for rate of reaction, depending on whether volume or mass, is being measured
- This is because, the mass of a solid product is often measured in grams; the volume of a gaseous product, is often measured in cm^3
Why is there more than one unit, for rate of reaction ?
- there’s more than one unit, for rate of reaction because:
- if a gas was being given off during a reaction, you could: take some measurements, and then work out the volume being given off per second, at any particular time during the reaction.
- ; rate usually measured, by looking at how fast the concentration of one of the reactants is falling at any one time.
Explain why many collisions, don’t lead to a chemical reaction
- many collisions don’t lead to a chemical reaction because:
- the particles may not collide with enough energy or in the correct orientation
- This is because, the particles need to be moving towards in each other, and facing each other- so they don’t simply bounce off each other, which would result in an unsuccessful collision.
- Fill in the gaps: if _______ area increases—> more __________ are available to react——> more successful collisions——> and the rate of reaction ________.
This is because, if surface area increases—> more particles are available to react——> more successful collisions——> and the rate of reaction increases.
How can you remember, how temperature affects rate of reaction ?
- temperature
- speed
- number of collisions
- energy
- greater than Ea
- chance of successful collisions
How can you remember, how pressure affects rate of reaction ?
- pressure
- pushes and squashes
- successful collisions
How can you remember, how concentration affects rate of reaction ?
- concentration of reactants in solution
- more particles available
- more frequent
