State the main postulates of the collision theory​

There are three important parts to collision theory, that reacting substances must collide, that they must collide with enough energy and that they must collide with the correct orientation. The reacting species must collide in an orientation that allows contact between the atoms that will become bonded together in the product.

reaction rate∝(collisions/time)

answer: semi-infinite solid initially at a uniform temperature of 400 ◦c is cooled at its surface by convection. the cooling fluid at a constant temperature of 200 ◦c has a convective coefficient (ha) of 250 w/m2.k. the physical properties of the solid: k = 20 w/m.k and α = 4 * 10-5  m2/s. using δx = 0.04 m and δt = 10 s. write the finite difference equations describing the transient heat transfer of the first five δx and the temperature profile after 30 s.