PHYSICAL CHEMISTRY BASICS PART 10: REACTION MECHANISM How does reaction mechanism affect reaction rate?
���� � �. �� � ����� → ����� → �����
�� =? 226Ra-Activity: 30 Bq What are the kinetic parameters of the simple reaction � → �?
����� → ��� = ��� + ��� (�� − 5.3) � � = �. �� [���� ]� � � � �.�� � [�����] = [�����]� � �
�� ���.� ��� �� � � = �. �� �� � �� � (�� − 5.7) #������� #������������������� #�������������� How do chemical reactions work at an atomic level? ������ � ������ �������� + ��� → (���)����
��������� � ������� �
� + � → � − �
� − � → � + �
� − � → �
�� �� � + � ⇄ �� → � + �
�� #������������������ #��������� What is an elementary reaction in chemical kinetics?
� + � → � − � � �� � = = � � � �� �
� − � → � + � � �� −�′ = = −� �� �� �
� − � → � � �� −� = = � �� �� �
#������������ #������������� (�� − �. 27) True or False?
The dimerization of two polymer chain radicals proceeds as an elementary step of radical polymerization according to a ...
A: B: 2th order 1st order kinetics. kinetics
C: D: 1.5nd order 2nd order kinetics kinetics Which mechanisms can we combine from 2 elementary reactions?
� → � � � ⇄ � � → � � (�� − 8.1)
� → � � �′ � → � → � Max Bodenstein
* Magdeburg 1871 � → � † Berlin 1942 (�� − 9.1)
#������������������ � → � � �′ � ← � → � #������������������� � → � (�� − 10.1) #���������������� � What is the mechanism of a reversible reaction? � ⇄ �
� � ∝ −� − ������� ⇄ � − � − �������
� (�� − 8.2)
� ∝ � = − � = � [∝] �� → (�� − 8.3)
� ∝ � = � = � [�] �� ← (�� − 8.4) #��������������� #��������������� � How to model a reversible reaction? � ⇄ �
�
#���� #������������ � How do we determine the rate law for a reversible reaction? � ⇄ �
� � � � = � = � [�] �� ←
� � = � � − � [�] (�� − 8.5) ��
� � #������ � = − � = � [�] �� → #���� � How do concentrations change over time? � ⇄ � � � � � � (�� − 8.21) � � = � + � � � + �
� = � � − �
� [�]��
� ��
�
#����������������� � Thermodynamics and kinetics of a reversible reaction � ⇄ �
�
�� − �� = ∆�� (�� − 8.28)
� �� � � = = � [�] = � [�] �� � #������������������ �� �� �� � (�� − 8.26) (�� − 8.27) True or False? At dynamic chemical equilibium... A: …the rate of B: … …the rate the forward constant of the reaction is equal forward reaction is to the rate of the equal to the rate reverse reaction constant of the reverse reaction C: …the activation energy of the forward reaction is equal to the activation energy of the reverse reaction How does temperature affect a reversible reaction?
�� + �� ⇄ � ��
� � ��� Max Bodenstein �� � �� � 1871 - 1942 � �. �� �� �. �� �� 129 ��� � ��� � � � � � � �. �� �� �. �� �� 77.8 ��� � ��� � � � � � � �. �� �� �. � �� 54.9 ��� � ��� � (�� − ���. 8.1)
#����������������� Max Bodenstein * Magdeburg 1871 #��� ����† �Berlin��������������� 1942 How does temperature affect rate constants and equilibrium constant?
Hinreaktion : k(298 K) = 3,7 1/h; EA=9.86 kJ/mol; Rückreaktion: k(298 K) = 2,7 1/h; EA=19.7 kJ/mol;
�� − ��. �� − (�� − ��. ��) � �′ � → � → � What is the mechanism of a consecutive reaction?
�� ��′ ′ �� � →→ ��� → → � �� (�� − 9.1)
� � � = � = � [�] �� � (�� − 9.2) #������������ #��������������� � � � = − � = �´ [�] �� #����������� �� (�� − 9.3) � �′ How to model a concecutive reaction? � → � → �
#���� #������������ � �′ How do we determine the rate law for a consecutive reaction? � → � → �
� � � = � = � [�] �� �
� � = � � − �´ [�] �� (�� − 9.5)
#������ � � � = − � = �´ [�] �� #���� �� � �′ How do concentrations change over time? � → � → �