Reaction rate
Everything that changes a reaction's rate is explained in three ways and there is no fourth: either more collisions per second, or collisions carrying more energy, or less energy needed to react. Raising the temperature does the first two at once, which is why it has the biggest effect. Grinding a solid multiplies the surface in contact. Concentrating puts more particles per litre; diluting does the opposite. Cooling slows everything, which is why food lasts longer in the fridge: cold kills almost nothing, it just makes spoiling take days instead of hours. A catalyst is the third route: it opens a path that costs less energy, like a tunnel instead of a mountain pass, it takes part and comes out whole, so a pinch serves for tonnes. The body's enzymes are catalysts and without them almost no reaction of life would run at a useful rate. And a warning: rate does not change how much product comes out in the end, only how long it takes. That is decided by the equilibrium.
Where this sits
- Comes after
- Reactions that give and take heat
- Opens up
- Chemical equilibrium
Exercises from this rung
Generated by the app, from easiest to hardest
Why does adding a catalyst speed up a reaction?
- Because it opens a route that needs less energy
- Because there are fewer particles per litre and they collide less
- Because particles collide more often and harder
- Because there is far more surface in contact
Why Because it opens a route that needs less energy. Everything that changes a reaction's rate is explained the same way: either more collisions per second, or collisions with more energy, or a lower energy cost to react. There is no fourth route.
easierWhy does raising the temperature speed up a reaction?
- Because there is far more surface in contact
- Because there are fewer particles per litre and they collide less
- Because it opens a route that needs less energy
- Because particles collide more often and harder
Why Because particles collide more often and harder. Everything that changes a reaction's rate is explained the same way: either more collisions per second, or collisions with more energy, or a lower energy cost to react. There is no fourth route.
in betweenWhat makes a catalyst different from a reactant?
- That it comes out unchanged at the end
- That it makes the reaction exothermic
- That it gives the reaction energy
- That it increases how much product comes out
Why It takes part and comes out whole, so a pinch serves for tonnes. It adds no energy and does not change how much product comes out: it opens a different route that costs less energy, like a tunnel instead of a mountain pass. The body's enzymes are catalysts, and without them almost no reaction of life would run at a useful rate.
harder