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Description
Flashcards by milicevic.marija, updated more than 1 year ago
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Created by milicevic.marija
about 9 years ago
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| Question | Answer |
| Define the term 'rate of reaction' | The decrease in the concentration of reactants per unit time. |
| Describe the collision theory | Particles must collide in order to react. This is because chemical reactions involve breaking and making bonds. Breaking bonds is not possible without collisions. |
| What do the collisions need? | Collisions need to have a minimum energy for a process to be possible, known as the activation energy. Collisions myst also have the right orientation. |
| Define activation energy | The minimum amount of energy required for reaction to take place. |
| What is particle size? | Bulk particles of a substance, for example, powder |
| What is the effect of changing bulk particle size? | By making them smaller, it exposes more reactive sites to the reacting compound. Increasing the possibility of successful collisions and rate of reaction. |
| What is the effect of temperature change on reaction time? | The particles travel faster at an increased temperature and will collide more frequently. This has the effect of increasing the rate. It also causes particles to have the required activation energy. Distribution will change. |
| What is the effect of changing concentration? | Increasing the concentration of reactants increases the number of collisions per unit time and hence the rate. |
| How do catalysts affect the rate of reaction? | They provide an alternative route to the products which has a lower activation energy. This means that there are greater numbers of particles with the required activation energy and hence a faster reaction rate is possible. |
| Explain how reactions can occur by more than one step | Few reactions involve just one step although one step in the reaction determines the reaction time, rate determining step. Actual process of chemical reactions involve many collision steps and these are called mechanisms. These steps usually happen at different rates. |
| What is the rate determining step? | The slowest step has the greatest influence on the overall rate and is called the rate determining step. |
| Define rate constant | A measure of how fast the reaction is. |
| Define rate of reaction | The numbers to which the concentrations are raised in the rate expression. Shows number of particles of this reagent involved in the rate determining step of the mechanism. |
| How do you calculate the total order of the reaction? | Find the sum of the individual orders (X+Y) |
| Formula for rate expression | Rate = K[A]^X[B]^Y |
| What is the unit for order 1? | s^-1 |
| What is the unit for order 2? | dm^3mol^-1s^-1 |
| What is the unit for order 3? | dm^6 mol^-2 s^-1 |
| What are all substances made of? | Particles |
| What are mechanisms? | Distinct stages a reaction must pass through |
| What is the rate determining step? | The slowest step that occurs. |
| What is molecularity? | The number of particles involved in the rate determining step of the reaction |
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