CHEM.13.C

Previous Next
The student is expected to classify processes as exothermic or endothermic and represent energy changes that occur in chemical reactions using thermochemical equations or graphical analysis; and
1666 TEKS header image

Knowledge and Skills Statement

Science concepts. The student understands the energy changes that occur in chemical reactions.

Endothermic Reactions:
Endothermic reactions require heat to occur. One reaction of industrial importance is steam-methane reforming, which is a first step in the production of hydrogen, ammonia, or methanol from natural gas. The basic reaction is CH4 + H2O -> 3H2 + CO. Endothermic reactions can be shown on a graph like the one seen below.

The energy stored in molecular bonds is greater in the products than in the reactants. A Once the initial activation energy requirements were overcome the reaction proceeded resulting in the product “C”. As the molecular bonds formed they absorbed heat energy
Image 1 source: https://upload.wikimedia.org/wikipedia/commons/7/77/Endothermic_Reaction.png


Exothermic Reactions:
Exothermic reactions release heat. Hand warmers are an example of an exothermic reaction. The chemical equation that represents the reaction is 4 Fe + 3O2 → 2Fe2O3 ΔH = -1648 kJ/mol. Exothermic reactions can be shown on a graph like the one seen below.
 

The energy stored in molecular bonds is greater in the reactants than in the products. Once the initial activation energy requirements were overcome the reaction proceeded resulting in the product “C”. As the molecular bonds formed they released heat energy.
Image 2 source: https://upload.wikimedia.org/wikipedia/commons/a/a6/Exothermic_Reaction.png

a chemical change that occurs when two or more substances combine to form a new substance; the rearrangement of atoms to produce new compounds

reactions in which the reactants absorb heat or light energy from the surroundings to form products

a measurable quantity that describes how much change can occur within a system

reactions in which energy is released in the form of light or heat

Research

Turk, Fatma and Muammer Calik. "Using Different Conceptual Change Methods Embedded Within 5E Model: A Sample Teaching of Endothermic – Exothermic Reactions." Asia-Pacific Forum on Science Learning and Teaching 9, no.1. (2008): 3-10. ied.edu.hk.

Summary: 

Research

Borda, Emily, Todd Haskell, and Andrew Boudreaux. "Cross-Disciplinary Learning: A Framework for Assessing Application of Concepts Across Science Disciplines." Journal of College Science Teaching 52, no. 1 (2022): 83-92.

Summary:  We have focused our discussion on energy in physics and chemistry, but a cross-disciplinary approach could be adapted to other concepts and contexts. We argue that assessments that focus narrowly on a single disciplinary context can be supplemented with approaches that explicitly target ways of making connections across disciplines.