Chemistry Chemical Kinetics

For the reaction C? H? → C? H? + H? , calculate the enthalpy change (ΔH).

ΔH = [Bond energy (C-C) + 6 * Bond energy (C-H)] - [Bond energy (C=C) + 4 * Bond energy (C-H) + Bond energy (H-H)]

ΔH = 347 + 2 (414) - 611 - 436 = 128 kJ/mol.

The change in entropy for the following processes is negative (ΔS = -ve), indicating an increase in order:

Water (l) → Ice (s) at 0°C

H? O (l) → Ice (s) at -10°C

N? (g) + 3H? (g) → 2NH? (g)

Adsorption

Unimolecular Reactions might seem to not participate in the collision theory due to the presence of only a single molecule. In such cases, the molecule is activated by external forces such as heat, light, electricity, or by colliding with the walls of the container. This force charges the molecule enough to break the activation barrier and result in an effective collision.

Kt = 2.303 log? (A? /A? )
K * 570 = 2.303 log? (100/32)
K = [2.303 / 570] [log?10² - log?2? ]
K = [2.303 / 570] [2 - 5 * 0.301] = [2.303 / 570] * 0.495 = 0.002 = 2.0 * 10? ³ s? ¹
Ans = 2

Industries manily select an optimal temperature which is high enough to increase the reaction rate (molecules colliding with each other at higher fequencies) and at the same time is balanced to avoid any side effect. This effectively yields high quality production without any wastage or leading to harmful results while ensuring safety of the consumers too.

For A
0.693/300 = (2.303/t) log (A? /A? )

For B
0.693/180 = (2.303/t) log (B? /B? )

Given A? = B? & A? = 4B?
Substituting & solving we get t = 900 s

To understand the phenomenon behind this, have a close look at the formula of the first order reaction.

t1/2 = 0.693/k

Here, we can see that the half life is only dependent on k (rate constant) since there is no [A]' in the formula. Hence, we can easily conclude that the half life of a first order reaction is independent of the initial concentration [A]'.

log (k? /k? ) = (Ea / 2.303R) [1/T? - 1/T? ]
log (3.555) = (Ea / (2.303R) [1/303 - 1/313]
1.268 * 8.314 * 303 * 313 = 10Ea
So, Ea = 100 kJ

k = Ae? Ea/RT
ln (K? /K? ) = (Ea/R) [1/T? - 1/T? ]
ln (5) = (Ea/8.314) [1/300 - 1/315]
1.6094 = (Ea/8.314) [15 / (300 * 315)]
Ea = 84297 J