Rates and Energy Flashcards
What two equations can be used to work out the rate of reaction?
Amount of reactant used ÷ time
Amount of product formed ÷ time
How can the average rate of reaction be found?
By measuring the time it takes for a certain amount of solid to appear in a solution
By measuring the amount of time it takes to collect a certain amount of gas
How can the rate of reaction at any given time be found?
From the gradient of the line on a graph of amount of product against time
What is the relationship between rate and time?
Rate is inversely proportional to time
How could a graph showing the rate of reaction be produced?
By measuring…
- Mass/volume of gas produced
- Changes in colour
- Change in concentration
- Change in pH
…over time
What is collision theory?
Chemical reactions can only happen if particles collide with sufficient energy
What is activation energy?
The minimum amount of energy for particles to collide/to start a reaction
What can increase the rate of reaction?
- Temperature
- Concentration of solutions
- Pressure of gases
- Surface areas of solids
- Using a catalyst
Why do powders react faster than large pieces of solid?
- They have a larger surface area
- This means that there are more collsision in the same space of time
- Therefore, the rate of reaction is faster
Why does increasing temperature increase the rate of reaction?
- Increasing the temperature increases the speed of particles
- This means they collide more frequency, increasing the rate of reaction
- It also means they collide with more energy
- This also increases the rate of reaction
Why does a small change in temperature have a large effect on the rate of reaction?
Because it increases both the speed of the collisions and energy of the particles
Why does increasing concentration increase the rate of reaction?
- Particles in a solutions are moving randomly
- If the concentration increases, there are more dissolved in the same volume
- This means the particles are closer together so collide more often
- This therefore increases the rate of reaction, because the frequency of reactions is increased
Why does increasing pressure increase the rate of reaction?
- There are more molecules/particles in the same volume
- This means they collide more frequently
- Therefore the rate of reaction is increased
What happens to a catalyst during a chemical reaction?
Nothing, it is not used up
What do solid catalysts normally have and why?
A large surface area to make them as efficient as possible
Why do different reactions need different catalysts?
Catalysts often only work with one type of reaction
Why does using a catalyst increase the rate of reaction?
- The activation energy is lowered
- This means that more of the collisions between particles result in a reaction
- Therefore the rate of reaction is lowered
What are many of the catalysts used in industry made of?
Transitions metals or their compounds
What are the advantages of using catalysts in industry?
- They do not need replacing very often
- They reduce the time and energy needed for a reaction
- This helps to reduce osts and environmental impact
- If fossil fuels are burned to provide the energy for reactions, then catalysts will help conserve resources and reduce pollution/global warming
What are the disadvantages of using catalysts in industry?
- Some transition metals and their compounds are toxic and may cause harm if they get into the environment
- They are expensive
- Different ones are needed for different reactions
What two areas of research offer possibilities for new or better catalysts?
Nanoscience and biological catalysts
How is energy transfered in chemical reactions?
When bonds are broken or made
What are exothermic reactions?
Reactions that transfer energy to the surroundings
This energy is often transfered as heat, so the surroundings heat up
Give some examples of exothermic reactions
- Combustion, such as burning fuels
- Oxidation reactions, such as respiration
- Neutralisation reactions
What are endothermic reactions?
Reactions that take in energy from the surroundings
What are the two ways to show that a reaction is endothermic?
Either causes a decrease in temperature or requires a constant supply of energy
When some solid compounds are mixed with water, why might the temperature decrease?
Because an endothermic reaction is taking place as they dissolve
Give an example of a type of reaction that needs to be heated continuously to keep it going
Thermal decomposition
What is the relationship between the forward and reverse reactions in reversible reactions?
They are equal but involve opposite energy transfers
A reaction that is endothermic one way will be exothermic the other
How much energy is released by the forward and reverse reactions of a reversible reaction?
The same amount of energy is released by both reactions (forwards and back)
What type of reaction occurs when blue copper sulfate crystals are heated?
Endothermic
What type of reaction occurs when water is added to anhydrous copper sulfate solution?
Exothermic
Draw a balanced symbol equation showing how hydrated copper sulfate is reacted to make anhydrous copper sulfate
CuSO4 • 5H2O ⇌ CuSO4 + 5H2O
Hydrated copper sulfate ⇌ Anhydrous copper sulfate + water
What can exothermic reactions be used to do and give an example of a product that uses this
They can be used to heat things
For example, a hand warmer
What can endothermic reactions be used to do and give an example of a product that does this
They can be used to cool things
For example, cold packs
Suggest the advantages and disadvantages of a re-usable hand warmer compared with a single use handwarmer
Advantage: Less waste/less matierals/resources used
Disadvantage: Has to be heated or needs energy to be used again, slower reaction, smaller temperature rise
Suggest the advantages and disadvantages of a chemical cold pack compared with using an ice pack
Advantages: Can be used anywhere, can be stored easily
Disadvantage: Can only be used once, more waste, possibly more hazardous
