Section 7 - Rates of reaction and energy changes - Collision Theory, catalysts, endothermic/exothermic reactions and bond energies Flashcards
3 factors that affect rate of reaction?
Temperature, concentration (or pressure for gases) and size of particles (for solids)
What is collision theory?
Particles must collide with enough energy in order to react
2 things rate of a chemical reaction depends on in collision theory?
- Collision frequency of reacting particles. More successful collisions = faster reaction
- Energy transferred during a collision. Particles need to collide with at least the activation energy for collision to be successful
What is activation energy?
Minimum energy that particles need to react when they collide; for bonds to break and reaction to start
How does increasing temperature increase rate of reaction?
When temperature increased, particles gain more energy so move faster and more chance of collision and with enough energy, thus more successful collisions
How does increasing concentration (or pressure) increase rate of reaction?
If solution is more concentrated, means more particles of reactant in same volume so collisions more likely, thus rate increases. In gas, increasing pressure means that particles more crowded, meaning frequency of collisions will increase.
How would smaller solid particles (or more surface area) increase rate of reaction?
Increased sa:v ratio means particles around it will have more area to work on and have increased chance of colliding with it so frequency of collisions will increase
What is a catalyst and what does it do? How do they work?
A substance that increases rate of reaction without chemically changed or used up in reaction.
They work by decreasing activation energy needed for reaction to occur, by providing alternative reaction pathway that has a lower activation energy
What is an enzyme and what does it do? 3 examples of reaction catalysed by enzymes?
Biological catalyst that catalyse chemical reactions in living cells. Reaction include respiration, photosynthesis and protein synthesis
What are enzymes from yeast cells used in and what do they do in this reaction?
Enzymes from yeast cells used in fermentation process which is used to make alcoholic drinks. They catalyse reaction that converts sugars into ethanol and CO2.
Difference between endothermic and exothermic reactions and what happens to temperature of surrounding for each?
Exothermic - gives out energy to surroundings, which rises in temperature, usually in form of heat
Endothermic - takes in energy from surroundings, which falls in temperature, usually in form of heat
What is the reaction profile like for exothermic reaction compared ti endothermic reaction?
Exo - products are at lower energy than reactants
Endo - products are at higher energy than reactants
In reaction profiles, what does difference in height represent?
The energy taken in or given out during reaction
Where is the activation energy on a reaction profile?
The energy difference between reactants and highest point on curve
When won’t an exo/endo reaction occur?
If energy input is less than activation energy, there won’t be enough energy to start reaction
