Activation energy of a reaction is

What is Activation Energy $(E_a)$? Explain the reaction profile graph for activation energy and discuss the probability of effective collisions.

For a reversible chemical reaction where the forward process is exothermic,which of the following statements is correct?

For a first order chemical reaction,

For an exothermic reaction $X \rightarrow Y$,the activation energy is $30 \ kJ \ mol^{-1}$. If the enthalpy change $(\Delta H)$ for the reaction is $-20 \ kJ \ mol^{-1}$,then the activation energy for the reverse reaction is . . . . . . $kJ \ mol^{-1}$.

For a reaction at a given temperature $T$,the rate constant $K$ is given by the Arrhenius equation. What is the value of $\lim_{T \to \infty} \log K$?