Chemistry: Kinetics
This flashcard set explains the conditions required for chemical reactions to occur, focusing on collision theory, activation energy, and reasons why many collisions are unsuccessful. It also defines the rate of reaction and its standard units.
When can reactions occur
Only when collisions take place between parties having sufficient energy and correct orientation
Key Terms
When can reactions occur
Only when collisions take place between parties having sufficient energy and correct orientation
What is this sufficient energy called
The activation energy
Activation energy
The minimum energy required to start a reaction by breaking of bonds
Why do most collisions not lead to a reaction
may be insufficient energy
- orientation may be incorrect
Rate of reaction
The change in concentration of a substance in a given time
What are the units of rate
mol dm-3 s-1
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| Term | Definition |
|---|---|
When can reactions occur | Only when collisions take place between parties having sufficient energy and correct orientation |
| The activation energy |
Activation energy | The minimum energy required to start a reaction by breaking of bonds |
Why do most collisions not lead to a reaction |
- orientation may be incorrect |
Rate of reaction | The change in concentration of a substance in a given time |
What are the units of rate | mol dm-3 s-1 |
Why does the rate decrease as the reaction proceeds | The concentration of reactant falls |
What is the rate at a particular time equal to | The gradient at that time |
What is the correlation between concentration and rate | Increasing the concentration increases the rate |
Why does increasing concentration increase rate |
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What is the correlation between pressure of gases and rate | Increasing the pressure increases the rate |
Why does increasing pressure gases increase rate |
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What is the correlation between increasing SA of solids and rate | Increasing SA increases rate |
Why does increasing SA of solids increase rate |
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What is correlation between temperature and rate of reaction | Increasing temperature increases the rate |
Why does increasing temperature increase rate |
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What does adding a catalyst do to rate of reaction | Increases it without it being used up |
Why does adding a catalyst increase rate of reaction |
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Experiment between HCl and CaCO3 to show effect of conc on RoR | Add CaCO3 to HCl Collect CO2 produced in a gas syringe Record volume of CO2 at regular intervals Produce graph of volume of CO2 against time |
What would a curve look like with same number of moles of acid but higher concentration | Steeper curve but levels of at same volume of CO2 |
What would curve look like with half moles acid but same conc | Same steepness of curve but half final volume of CO2 |
What does the reaction between sodium thiosulfate and hydrochloric acid produce | A precipitate of sulfur, sodium chloride and sulfur dioxide |
How can the rate of reaction between sodium sodium thiosulfate and hydrochloric acid be monitored | Measure time taken for cross to disappear from view Cross obscured by PPT of sulfur |
What is measuring time taken for cross to disappear called | Initial rate method |
How can temp be known as accurately as possible in reaction between sodium thiosulfate and hydrochloric acid | Measure initial and final temp- take and use an average |
What could be used to prevent SO2 escaping from the reaction | Put a lid on the reaction vessel to minimise escape of CO2 |
Why is a STOP bath used in reaction between sodium thiosulfate and hydrochloric acid | Both acid and sulfur dioxide can be neutralised |
What is the independent variable in the reaction between sodium thiosulfate and hydrochloric acid | Temperature |
What is the dependent variable in the reaction between sodium thiosulfate and hydrochloric acid | Time |
Why is the hazard associated with sulfur dioxide in this investigation considered to be low | Amount of SO2 low because solutions are dilute SO2 is soluble- doesn't all escape as a gas |
Why do the particles in a particular sample have a spread of energies when the samples collide | Energy is exchanged between them |
What does the Maxwell-Boltzmann distribution show | The distribution of energies of the particles within a sample |
What is the important feature of the maxwell boltzmann distribution that is seen at the origin of the graph | No particles have no energy |
What is the important feature of the maxwell boltzmann distribution that is seen at the end of the graph | The curve doesn't meet back with the x axis- no maximum energy |
What is the important feature of the maxwell boltzmann distribution at the highest point of the graph | The most likely every is not very high |
What does the shaded area represent on a maxwell Boltzmann distribution | Particles which will successfully collide |
How is the peak on a maxwell distribution curve at a higher temperature different | It's lower and to the right |
What is the difference between most probable energy in a maxwell Boltzmann distribution curve at a higher temp | The most probable energy is higher |
What is the change in area under the curve maxwell botlzmann at higher temp | Area under curve remains same |
How is the shaded area different in maxwell Boltzmann curve at higher temp | Shaded area now much larger as far more particles have energy equal to or greater than activation energy |
Why does a small temperature increase lead to a large increase in rate | Far more particles will now have energy greater than or equal to activation energy so far more successful collisions |
What is a catalyst | A substance which increases the rate of a chemical reaction without being changed in chemical composition or amount |
What does a catalyst provide | An alternative reaction route with a lower activation energy |
What is lowered and what is unchanged in the presence of a catalyst | Activation energy lowered but enthalpy not changed |
What does a maxwell Boltzmann distribution look like with a catalyst | Shaded area is bigger so more molecules have energy greater than or equal to activation energy More collisions are successful so rate of reaction increases |