3.6 - Rates of reaction Flashcards
Define rate of reaction
how fast reactant used up/product formed
Equation for rate of reaction and its units
change in conc/time
units: moldm-3s-1
Conditions for a reaction to occur
reacting particles must collide with:
- correct orientation
- sufficient energy
How does increasing concentration affect rate?
- more particles in same volume
- more frequent collisions per unit of time
- increased rate
How does increasing pressure affect rate (gases)?
- molecules closer together
- more frequent collisions per unit of time
- increased rate
Describe effect of decreasing pressure on rate
- decreases rate
- decreased conc of molecules/less molecules per unit volume
- less frequent collisions per unit of time
How can reaction progress be monitored?
- removal of reactant
- formation of product
Define catalyst
- substance that changes rate of a chemical reaction without undergoing any permanent change
- provides alternative reaction pathway w/ lower Ea
Define homogeneous catalyst
same physical state as reactants
Define heterogeneous catalyst
different physical state to reactants
When may it be difficult to classify a catalyst into homogeneous or heterogeneous?
when reactants have different physical states
Benefits of catalysts
- lower temps/pressures can be used
- less energy/electricity required
- lower energy costs
- less fossil fuels combusted so less environmental damage via CO2 emissions
What does sustainability require?
- high atom economies
- few pollutants
Features of Boltmann distribution
- curve starts at origin (no molecules have 0 energy)
- area under curve = total no. of molecules
- doesn’t meet x-axis (no maximum energy)
Effect of increasing temperature on Boltmann distribution
- peak lower and shifted to right
- more molecules have energy greater than Ea
- greater proportion of collisions exceeding Ea as molecules have more energy and move faster means increased rate
