Final answer:
The symbol 'Pt' over the arrow in a chemical equation indicates platinum is used as a catalyst. It signifies that the reaction proceeds with the aid of platinum, which accelerates the reaction without being consumed.
Step-by-step explanation:
In a chemical equation, the symbol 'Pt' placed over the arrow (→) typically means that platinum is being used as a catalyst in the reaction. A catalyst is a substance that increases the rate of a chemical reaction without being consumed in the process. The arrow in a chemical reaction represents the conversion of reactants to products, and symbols written above or below it provide additional information about the reaction conditions.
For instance, if a reaction is written as:
[Reactants] →[Pt] Products
This indicates that the reactants convert to products in the presence of a platinum catalyst. Other symbols such as 'A' may indicate that the reaction needs to be heated, but in this case, 'Pt' signifies the involvement of platinum as a catalyst.
Chemical equations outline the stoichiometry of the reactants and products, which means they show the mole ratios of the substances involved according to the balanced equation.