hess' law pdf

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. 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 … <8S�L� �������|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�? endobj 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. <>>> endobj 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. endobj Calculate ∆H for the reaction: C2H4 (g) + H2 (g) → C2H6 (g), from the following data.

Hess’s Law For a chemical equation that can be written as the sum of two or more steps the enthalpy change for the overall equation equals the sum of the enthalpy changes of the individual steps The enthalpy change for the reaction of NO 2 to produce N 2 O 4 can be determined by using a two-step path. �q�~�����?���g��4�Mz\87��1c�N�}�[2f��3v`�Ɓ�r��v���}����z�w�����Z�'����b� �5��`VdU����bV�߳���_���Y�l5g�r��p����㾙�~~�(yq_�������;aؓ9j�O�t!�VN�q"J�+7�uS�����i�q/��NX�^*��`�җ�f������-c�Y�TV_��,�_�ن��0���ˢfMɦ2�����k������H�V�8��Z�������~�1�j�.

It says that the heat liberated by a process doesn't depend on how the process happens (only on the starting and ending states: in other words, it's a state function).

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. %PDF-1.5

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Net result = same. Hess’s Law For a chemical equation that can be written as the sum of two or more steps the enthalpy change for the overall equation equals the sum of the enthalpy changes of the individual steps The enthalpy change for the reaction of NO 2 to produce N 2 O 4 can be determined by using a two-step path. 3 0 obj

endobj Example of Hess’s Law •Sulfur burned in oxygen will initially form SO2. 4 0 obj 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.

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x��Z�n�8}����"Qt!uO{{v;�L��0���$�qKiI���UER�d�fg1�-�.�:u�(�]ݳ�뫻�/?3w�`�?/�������c������|�������g. 4 0 obj ;!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�. 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). 3 0 obj

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Hess’ Law Start Finish • ΔH1 = ΔH2 + ΔH3 or • ΔH1 = ΔH4 + ΔH5 +ΔH6 Both lines accomplished 2 0 obj stream %PDF-1.5 1 0 obj

<> Hess’s Law & Standard Enthalpy of Formation Honors Chemistry Use Hess’s Law for Questions 1-4: 1.

View Lesson 4 - Hess' law.pdf from CHEMISTRY 4UO at Fletcher's Meadow Secondary School. [?� �+IXeM�g���sJ����Zt\�|٭�4�����%H�Z�8�=;D�m�-`�Mp&��I���F�$���� ��d�Y8d�0�5d88�5�����݃B�����V

<> 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.

%���� In the first step, NO 2 decomposes to N 2 and O 2. This example problem demonstrates strategies for how to use Hess's Law to …

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Hess’s law is a relationship in physical chemistry named after Germain Hess, a Swiss-born Russian chemist and physician. This law states that if a reaction takes place in several steps, then the standard reaction enthalpy for the overall reaction is equal to the sum of the standard enthalpies of the intermediate reaction steps, assuming each step takes place at the same temperature. endobj 2 0 obj

Hess' Law is an early statement of the law of conservation of energy (1840). <>/ProcSet[/PDF/Text/ImageB/ImageC/ImageI] >>/MediaBox[ 0 0 612 792] /Contents 4 0 R/Group<>/Tabs/S/StructParents 0>> 1 0 obj %����

<> Steps: For each reaction: 1) Check to see, if the compounds are on the correct sides of the reaction. x��=[�E������t]�k"A���j`fa�a��� b�߯]����r'H� ���r�\��e����:=z��_���G������GO����O�$ļ��o�����tjVjZ���6}���{�� <>>>

This lab will demonstrate Hess’ Law, which we learned in class and will help us further understand the concepts of thermochemistry.

4) Calculate the ΔH for our reaction: (+45.9 kJ) + (+74.9 kJ) + (+135.15) = +255.95 kJ

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