The half life period of a first order chemical reaction is 6.93 minutes. The time required for the completion of 99% of the chemical reaction will be (log 2=0.301) :

For a reaction $${1 \over 2}A \to 2B$$ rate of disappearance of ‘A’ is related to the rate of appearance of ‘B’ by the expression

A radioactive element gets spilled over the floor of a room. Its half-life period is 30 days. If the initial activity is ten times the permissible value, after how many days will it be safe to enter the room?

The energies of activation for forward and reverse reactions for A₂ + B₂ $$\leftrightharpoons$$ 2AB are 180 kJ mol⁻¹ and 200 kJ mol⁻¹ respectively. The presence of catalyst lowers the activation energy of both (forward and reverse) reactions by 100 kJ mol⁻¹. The enthalpy change of the reaction ( A₂ + B₂ $$\to$$ 2AB) in the presence of catalyst will be (in kJ mol⁻¹)