Rates of Reaction Flashcards
Explain how chemical reactions occur
- For chemical reactions to occur, reactant particles must collide with each other with enough energy to react
- The minimum amount of energy required for a reaction to occur is called the activation energy
- During successful collisions, this energy helps to break bonds, so that atoms can be rearranged to make new substances (the products of the reaction)
What are reactions that release energy called?
Exothermic Changes
What are reactions that take in energy to occur called?
Endothermic Changes
- These will not keep going unless energy is continuously supplied
When are reaction rates generally increased? - why?
- When energy increases
- When frequency increases (number of collisions in a certain amount of time)
When the energy is increased, more successful collisions will occur if more particles have the activation energy required
What affect does concentration have on reaction rate?
- Increasing the concentration of solutions increases the rate of reaction
There are more reacting particles in the same volume, so collisions occur more often
What affect does surface area have on reaction rate?
- Increasing the surface area to volume ratio increases the rate of reaction
There is more surface for collisions to occur on, so collisions occur more often
What affect does pressure of gases have on reaction rate?
- Increasing the pressure of gases increases the rate of reaction
The reactant particles are squeezed closer together, so collisions occur more often
What affect does temperature have on reaction rate?
- Increasing the temperature increases the rate of reaction
Reactant particles speed up and have more energy. Therefore, they collide more often and more particles have enough energy for a successful collision when they collide
What are catalysts?
Catalysts are substances that speed up chemical reactions without being permanently changed themselves, in mass or chemically, at the end of the reaction, and without altering the products
Explain how catalysts increase the rate of reaction, in terms of activation energy
It provides an alternative reaction route that requires less energy to start the reaction, so more reactant molecules have enough activation energy so more collisions are successful and thus the rate of reaction increases
What are enzymes?
Biological catalysts used in the production of alcoholic drinks
Explain the role of enzymes in the production of alcoholic drinks
Enzymes found in yeast catalyse the reaction in which glucose is converted into ethanol and carbon dioxide
Explain the role of catalysts in car exhausts
- In catalytic converters in car exhausts, the catalysts are platinum and palladium
- Their presence lowers the activation energy needed to convert harmful gases into harmless gases
- The metals used are expensive, but don’t need to be replaced as they are not used up
Why are reaction rates at the start the fastest? (concentration graph)
The concentration of reactants is the highest
How can we investigate reaction rates?
By measuring the amount of reactants or products changes with time
- Changes in the concentration
- Changes in the mass
- Changes in the volume
