Hess's Law
What is Hess's Law?
Hess’s Law states that the enthalpy change when going from reactants to products is the same whether the process occurs in a single step or in several, sequential steps. This piece of knowledge is very useful for measuring energy changes in reactions that we cannot study through calorimetry.
adapted from:
DiGiuseppe, M., Haberer, S., Salciccioli, K., Sanader, M., & Vavitsas, A. (2012). Nelson Chemistry 12 University preparation. Toronto, ON: Nelson Education Ltd.
Hess’s Law states that the enthalpy change when going from reactants to products is the same whether the process occurs in a single step or in several, sequential steps. This piece of knowledge is very useful for measuring energy changes in reactions that we cannot study through calorimetry.
adapted from:
DiGiuseppe, M., Haberer, S., Salciccioli, K., Sanader, M., & Vavitsas, A. (2012). Nelson Chemistry 12 University preparation. Toronto, ON: Nelson Education Ltd.
LESSON OVERVIEW (SPECIFIC EXPECTATIONS: D2.5, D2.6, D3.4)
Lesson Hook/Minds On:
Show students the ‘Thermochemistry’ song on YouTube. Hopefully it will get them laughing but also thinking. The chemistry knowledge is quite accurate and could serve as a great review for a test/exam. This will be especially beneficial for musical-rhythmic students who might be inspired to make some of their own songs to help them grasp these topics of thermochemistry. |
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Teaching Strategy:
Students will perform a virtual lab to try and find the enthalpy of combustion for magnesium. It might be necessary to use the computer lab if students do not have their own electronic devices. Students will have to try out different reactions in order to get the final product. They will also be required to construct an enthalpy diagram. This can be done in teams for interpersonal learners or individually (intrapersonal) as the virtual lab cuts out much of the time needed to conduct this investigation. There are also hints given if students are stuck. Students are also able to go back online and try the virtual lab at home whenever they want for extra practice or to help clarify the topic.
Students will perform a virtual lab to try and find the enthalpy of combustion for magnesium. It might be necessary to use the computer lab if students do not have their own electronic devices. Students will have to try out different reactions in order to get the final product. They will also be required to construct an enthalpy diagram. This can be done in teams for interpersonal learners or individually (intrapersonal) as the virtual lab cuts out much of the time needed to conduct this investigation. There are also hints given if students are stuck. Students are also able to go back online and try the virtual lab at home whenever they want for extra practice or to help clarify the topic.
Consolidation:
After the activity students should be given more opportunities to practise using Hess’s Law. Extra practise problems will help students refine their skills in solving these problems. One approach is to assign groups and give sample problems for all of the groups to do. At the end, each group can be asked to present their solution to one of the problems for their peers to see. Below is a link to a webpage with extra practice problems with solutions.
After the activity students should be given more opportunities to practise using Hess’s Law. Extra practise problems will help students refine their skills in solving these problems. One approach is to assign groups and give sample problems for all of the groups to do. At the end, each group can be asked to present their solution to one of the problems for their peers to see. Below is a link to a webpage with extra practice problems with solutions.
FOPP: Professional practice and commitment to students and student learning
Click below for a few resources that can be used in conjunction with a lesson to further demonstrate the concept of Hess's Law.