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ZingPath: Energy in Chemical Systems

Energy in Chemical Systems

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Energy in Chemical Systems

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Lesson Focus

Energy in Chemical Systems


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You get to find out about the energy stored in the bonds of molecules and how to predict if heat is released or consumed during a chemical reaction.

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Now You Know

After completing this tutorial, you will be able to complete the following:

  • Understand the energy changes that occur in chemical reactions.

Everything You'll Have Covered

What is enthalpy? How is enthalpy change calculated?

~ Enthalpy is energy that is stored in a system. During a reaction, energy is required to break the bonds of the reactants, and some energy is released during the formation of the product's new bonds. However, less energy is required to break the bonds than is required to form the bonds. Enthalpy change is calculated by subtracting the sum of the reactants' enthalpies from the sum of the products' enthalpies.

What is the standard enthalpy of formation?

~ The standard enthalpy of formation is the change of enthalpy that accompanies the formation of 1 mole of a substance from its constituent elements at 25?C and 1 atm.

Describe how the enthalpy change was found in the reaction involving methane in the animation.

~ To find the enthalpy change in the reaction involving methane, the equation is used. First, the sum of the products is found. The products are found to the right of the arrow in the reaction equation = -393.5 + 2(-241.8). Since there are 2 molecules of H?O, we must multiply the standard enthalpy of formation number for H?O by 2. Then, the sum of the reactants is subtracted from the sum of the products. The resulting equation is

This means that when 1 mole of methane reacts with oxygen, 802.2kJ of energy is released.

Tutorial Details

Approximate Time 2 Minutes
Pre-requisite Concepts Students should have a general understanding of the following terms: chemistry, endothermic, and energy.
Course Chemistry
Type of Tutorial Animation
Key Vocabulary chemistry, endothermic, energy