The following gas-phase reaction is carried out in a constant-volume isothermal batch reactor
$$A+B{\rightarrow}R+S$$
The reactants $A$ and $B$ as well as the product $S$ are non-condensable gases. At the operating temperature, the saturation pressure of the product $R$ is $40\:kPa$.
Initially, the batch reactor contains equimolar amounts of $A$ and $B$ (and no products) at a total pressure of $100\:kPa$. The initial concentrations of the reactants are $C_{A,O}=C_{B,O}-12.5$ mol/m$^{3}$. the rate of reaction is qiven by $(-r_{A})=0.08\:C_{A}\:C_{B}$ mol/m$^{3}.s$
The time at which $R$ just starts condensing, rounded to $1$ decimal place, is ____________ $s$.