If this is a kinetics problem, you need to know the order of the reaction, the integrated rate law, and the rate constant at 420 °C

Since you don’t state the specific problem, let's arbitrarily assume that the reaction is first order, the initial concentration of #"SO"_2"Cl"_2# is 0.0225 mol/L and that the rate constant is #2.90 × 10^"-4"color(white)(l) "s"^"-1"# at 420 °C.

Whenever a question asks, "How much is left after an amount of time?", that is a clue for you to use an **integrated rate law**.

The integrated rate law for a first order reaction is

#color(blue)(|bar(ul(color(white)(a/a) ln(A_0/A_t) = kt color(white)(a/a)|)))" "#

where

#"A"_0 = "concentration at time 0"#

#"A"_t = "concentration at time"color(white)(l) t#

#k = "rate constant"#

#t = "time"#

#t = 16.2 color(red)(cancel(color(black)("h"))) × (60 color(red)(cancel(color(black)("min"))))/(1 color(red)(cancel(color(black)("h")))) × "60 s"/(1 color(red)(cancel(color(black)("min")))) = "58 320 s"#

Then,

#ln("0.0225 mol/L"/"A"_t) = 2.90 × 10^"-4" color(red)(cancel(color(black)("s"^"-1"))) × "58 320" color(red)(cancel(color(black)("s"))) = 16.91#

#"0.0225 mol/L"/"A"_t= e^16.91 = 2.21× 10^7#

#"A"_t = "0.0225 mol/L"/(2.21× 10^7) = 1.02 × 10^"-9" color(white)(l)"mol/L"#