�������|zkn��p�P߼�nכ���}�n��ug��������7?�>47�ު�_�[�T��w�����}��)�I��.�ӳ�)�>�˓i��$*6��قK�2�/�eD�s��O�$��������*�,=R��/�2�U�u� y�,��e�۲�����G�W�z�P!�' ��w<6���pq�G�?~�F�]�_���#B�-@x���Fy����ˬ�v��>?E�>���ͯ`��������ۇ��O~���o����r /�;�% �Z��������{��� Cl��m֖�Ah�? 3.12 Hess’s Law Hess’s law states that total enthalpy change for a reaction is independent of the route by which the chemical change takes place Hess’s law is a version of the first law of thermodynamics, which is that energy is always conserved. stream View Lesson 4 - Hess' law.pdf from CHEMISTRY 4UO at Fletcher's Meadow Secondary School. ;!qf��H��������t3PW��լ7oX�a���(�+��ì��Q�"��-ӎT�0L�]�M₝��h"��s��~*p�!��S!%�e }v^�je@6%�d`�0-�@ڛ��[��� �f!�/i�w6����!����k!A̫1(a�Kϒ����w)�!��id�1�h�hddg�d� �g��[�o�M} G�ֱ���zj;d���cX�� V��\�iÿ��0I*Nj�u0Z���R��dHѲe'���sΣϐ\��W4�. x��=[�E������t]�k"A���j`fa�a��� b�߯]����r'H� ���r�\��e����:=z��_���G������GO����O�$ļ��o�����tjVjZ���6}���{�� %PDF-1.5

}�'���d��P�XcNlJi��Zݬ�IKTOxJ�T��ڕrn^l)���rl8�"��=�H1spo����i���A��A��/��^(�ύ�BYk~����\w���2��T��K$��a�k��>kDi��.F|�Qyi(�Լ!�3删�PC���? Step by Step: Hess’s Law (see at end for supplemental notes on ∆H formation with Hess's Law) The enthalpy change (ΔH r o) for a reaction is the sum of the enthalpy changes for a series of reactions, that add up to the overall reaction. kp�J7��ne|`� ����gl4�9�wu��������܂Wv4�6r@�I����.�*��|���H�ѫ����U��6{�^�G�\�Y����W�,"AOɭ�E���JN�L1�ўBmZ��t]:�P̪�b�A=o����8�KÛ�4'`���K�NwU,9#Œ�jP,��X�&�*�Q,R�=�ONK8�|�+���-�b&Z�*��OO����|��iT�BMܢ/G[ca$��j����;v �3? Materials: Power Macintosh or Windows PC 100 mL of water Vernier computer interface 4.00 g of solid NaOH Logger Pro ring stand Temperature Probe utility clamp 50 mL of 1.0 M NaOH stirring rod 50 mL of 1.0 M HCl Styrofoam cup 100 mL of 0.50 M HCl 250 … 3 0 obj 3 0 obj endobj Hess’s Law •ΔH overall = ΔH 1 + ΔH 2 + ΔH 3 … etc •If it takes several steps (or individual reactions) to get from one place to another, then you simply add the enthalpy values together to get to the overall enthalpy. 4) Calculate the ΔH for our reaction: (+45.9 kJ) + (+74.9 kJ) + (+135.15) = +255.95 kJ L��[�n^������|J��v�y����Ѱ{���O���u�+Pk�[��~���\���tP��g����^��" � ����V���L�UP�_EbYOb���˧],f��h�쀕}"�(�X�aso�$�ig��[2��۵$SwQnc2��&0���"���K��~G���Ŀ�����Ǡ�QQ&��=��̔C�U�e^]�̨ٺ/嘣F7���ͫ/o�xK��Qx��V <>/ProcSet[/PDF/Text/ImageB/ImageC/ImageI] >>/MediaBox[ 0 0 612 792] /Contents 4 0 R/Group<>/Tabs/S/StructParents 0>> Hess’s law is a relationship in physical chemistry named after Germain Hess, a Swiss-born Russian chemist and physician. [?� �+IXeM�g���sJ����Zt\�|٭�4�����%H�Z�8�=;D�m�-`�Mp&��I���F�$���� ��d�Y8d�0�5d88�5�����݃B�����V

This lab will demonstrate Hess’ Law, which we learned in class and will help us further understand the concepts of thermochemistry. Steps: For each reaction: 1) Check to see, if the compounds are on the correct sides of the reaction. This example problem demonstrates strategies for how to use Hess's Law to … Now we know we should really use enthalpy for this, not heat, because enthalpy is a state function, so this is true, while heat is a process. <>>> %���� Hess’s Law & Standard Enthalpy of Formation Honors Chemistry Use Hess’s Law for Questions 1-4: 1.

<> In the first step, NO 2 decomposes to N 2 and O 2. endobj

stream Hess's Law, also known as "Hess's Law of Constant Heat Summation," states that the total enthalpy of a chemical reaction is the sum of the enthalpy changes for the steps of the reaction.Therefore, you can find enthalpy change by breaking a reaction into component steps that have known enthalpy values. Unformatted text preview: Hess’ Law Start Finish • ΔH1 = ΔH2 + ΔH3 or • ΔH1 = ΔH4 + ΔH5 +ΔH6 Both lines accomplished the same result, they went from start to finish. 4 0 obj <> endobj <>>> endobj Hess’ Law Start Finish • ΔH1 = ΔH2 + ΔH3 or • ΔH1 = ΔH4 + ΔH5 +ΔH6 Both lines accomplished 4 0 obj 2 0 obj 2 0 obj <>

x��Z�n�8}����"Qt!uO{{v;�L��0���$�qKiI���UER�d�fg1�-�.�:u�(�]ݳ�뫻�/?3w�`�?/�������c������|�������g. 3) What cancels when you add the equations: 1 ⁄ 2 N 2 (g) ⇒ first and third equations C(s) ⇒ second and third equations 1 ⁄ 2 H 2 (g) on the left side of the third equation cancels out 1 ⁄ 2 H 2 (g) on the right, leaving a total of 3H 2 (g) on the right (which is what we want).