Explain how an increase in reactant concentration affects reaction rate, and calculate the moles of sulfur produced from 1.62g of sulfur in the reaction between Na2S2O3 and HCl.

According to the collision theory, an increase in the concentration of reactants affects the reaction rate as follows:

• An increase in concentration means there are more reactant particles per unit volume.
• This leads to an increase in the frequency of collisions between the reactant particles.
• Consequently, there will be a higher number of effective collisions per unit time (collisions with sufficient energy and correct orientation).
• A greater number of effective collisions per unit time results in an increased rate of reaction.

First, write the balanced chemical equation for the reaction:

From the equation, 1 mole of Na$_2$S$_2$O$_3$ produces 1 mole of S.

Molar mass of Sulphur (S) = 32.07 g/mol
Molar mass of Sodium thiosulphate (Na$_2$S$_2$O$_3$) = (2 $\times$ 22.99) + (2 $\times$ 32.07) + (3 $\times$ 16.00) = 45.98 + 64.14 + 48.00 = 158.12 g/mol

Given mass of S = 1.62 g

From the balanced equation, the mole ratio of Na$_2$S$_2$O$_3$ to S is 1:1.

Rounding to two decimal places:
The mass of the sodium thiosulphate used in experiment 1 is $\boxed{\text{7.99 g}}$.