What determines how fast a reaction happens?

What determines how fast a reaction happens is if one of the reactants is a solid, the surface area of the solid will affect how fast the reaction goes. This is because the two types of molecule can only bump into each other at the liquid solid interface, i.e. on the surface of the solid. So basically the larger the surface area of the solid, the faster the reaction will be.

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Explanation:

the maximum mass of nh3 is nh3 in grams