rate of reaction Flashcards
how do we measure rate of reaction
Rate of reaction is determined by measuring the formation of products or the depletion of reactants over time.
What are some factors that can be used to measure rate of reaction?
- the mass loss by reactants
- mass gained by products
- volume of gas
- pressure of gas
- colour intensity
- solution concentration
- pH
What are the factors that determine whether a reaction is successful or not
It must oriented correctly when colliding and have sufficient energy that is equal to or overcomes the activation energy
explain why correct orientation must be achieved for a successful reaction.
With correct orientation, it will lead to a reaction to likely occur as if the molecules were not in a favourable orientation, the molecules will simply bounce off each other. For example, hydrogen iodide gas into hydrogen gas and iodide gas. The favourable orientation would be the hydrogen and hydrogen atoms to collide while the iodine and iodine atoms collide.
how does the size of the molecule affect the reaction rate?
large or complex molecules where the reactive site only represents a small fraction of the molecule only have very small number of collisions.
molecules with extensive structures where the reactive sites are obscured from colliding with other reactant particles don’t always react to an appreciable extent
Explain why sufficient energy must be applied for a successful reaction.
Sufficient energy must be supplied to the reaction for the bond breaking and formation process. Enough energy must be supplied where the particles will have the equal amount or exceed the required activation energy.
What is the Maxwell Boltzmann distribution curve?
It is a probability distribution function that shows the range of the kinetic energies by the particles in a specific substance at a certain temperature.
The curve approaches but never touches the x axis showing that there will always be the chance of some particles possessing very high kinetic energy
The maximum of the graph does not show the maximum energy, it instead shows the energy possessed by most particles.
The area beneath the curve shows the amount of particles in the substance
What is activation energy?
The activation energy is the minimum amount of kinetic energy that is required for the particles to collide with to break the existing bonds in the reactants and allow the formation of the product.
What is an energy profile diagram?
An energy profile diagram is a graph that shows the reaction journey of individual atoms, ions and molecules.
What are the five main factors that influence rate of reaction
- surface area of reactants
- concentration of reactants in solution
- gas pressure
- temperature
- the presence of a catalyst
What is the effect the five main factors have on reaction rate?
- Generating a greater number of collisions both successful and unsuccessful per unit of time
- increasing the probability that any given collisions will be successful
How does surface area effect the rate of reaction?
Only in solids, only the particles at the surface are available to collide with other reactants and the number of particles at the surface depends on the surface area of the substance. When the size of the particles are reduced, the total surface area of the substance increases. This allows more reactant particles to collide, increasing the frequency of collisions, allowing a higher number of successful collisions per unit of time which increase the rate of reaction
How does concentration effect the rate of reaction?
Concentration is the number of particles per unit of volume. Higher the concentration of solutes dissolved in a solution increases the frequency of collisions. As there are more reactant particles in the same volume, it will result in a greater number of collisions. A certain percentage of these collisions will be successful resulting in a greater number of successful collisions per unit of time, hence an increase in reaction rate.
How does gas pressure effect the rate of reaction?
Pressure is the force per unit of area that the gas particles exert when they collide into the walls of their container. High gas pressure is the result of having an increase of gas particles in a given volume at a constant temperature. When more gas particles are added into a fixed volume, the frequency of collisions per unit of time will increase. Of these collisions, a certain percentage of these collisions will be successful resulting in a greater number of successful collisions per unit of time, hence an increase in reaction rate.
What is partial pressure?
For a mixture of gases, the total pressure exerted by the mixture is the sum of the individual pressures of the composite gases. These individual pressures when considered a mixture are known as partial pressures.
How does temperature effect the rate of reaction?
Temperature is the average kinetic energy that makes up a substance. The increase in temperature causes the particles to move, on average, with an increased speed causing more frequent collisions, both successful and unsuccessful. It also increases the percentage of these collisions satisfying the activation energy requirement for the reaction. This causes a higher percentage of the existing collisions to be more successful per unit of time, hence causing a faster reaction rate.
How does a presence of a catalyst effect the rate of reaction?
A catalyst works by providing an alternative reaction pathway with lower activation energy. A greater proportion of particles will have sufficient energy to equal or overcome the now reduced activation energy. This increases the probability of successful collisions resulting in a greater number of successful collisions per unit of time hence a quicker reaction rate.
What are catalysts?
- catalysts are specific to certain reactions
- what catalyses one reaction may not catalyse another
- catalysts are not consumed in the reaction and can be recovered and reused
- however, they can deactivated or poisoned at which point, they will no longer increase the reaction rate
- this alternate reaction pathway can be shown in a reaction energy profile
