in an experiament involving a reaction between two gases, the same number of moles are placed in two different syringes, What will be the difference in reaction rates

Generally, the factors that affect rate of chemical reactions include

temperature pressure (affects non-solid reactants) surface area of solid reactants concentration of reactants nature of reactants presence/absence of catalysts

From the above, it shows that some of these factors do not need to be considered when discussing rate of reaction of gases of equal moles as we have in the question.

The factors that will determine the difference in the reaction rates of the gases in the two syringes will just be temperature of the syringes (if the temperature of the syringes are not the same) and the pressure applied on the gases in the syringes (if the pressure applied to the syringes are not the same). If catalyst is introduced to one and not to the other, that will be increase the rate of the reaction in the one the catalyst is introduced and hence the reaction rate varies.

An increase in temperature and/or pressure will lead to an increase in the rate of reaction.