Why more surface is faster
The calculation and the experiment arrive at the same conclusion. But we have still not answered why.
The conclusion
As the surface area of the reactants increases, the rate of reaction increases.
The reason is collisions. As the surface area increases, the number of collisions the reactant particles make with one another goes up. More limestone particles are available for an acid molecule to meet at any one moment. So the amount of change in unit time goes up too.
In everyday life
In all sorts of everyday tasks we increase the surface area of the reactants in order to raise the rate of reaction. Assignment 17.3 asks for a list of such cases.
- Splitting firewood into small pieces
- Chewing food thoroughly
- Making detergents as powders
- Grinding medicines and pressing the powder into tablets
- Crushing limestone for cement manufacture
- Grinding metal ores before they are smelted
In the next section what we change is not the shape of the reactants but their temperature.