Lab 22: Student Exploration: Reaction Energy
Directions: Follow the instructions to go through the simulation. Respond to the quest... [Show More] ions and prompts in the orange boxes.
Vocabulary: calorimeter, chemical bond, endothermic, enthalpy, exothermic, Hess’s law
Prior Knowledge Questions (Do these BEFORE using the Gizmo.)
1. Two magnets are stuck together. What might you have to do to get them to separate?
2. Suppose you held two magnets a short distance apart, then let go. What would happen?
3. Think about the magnets in terms of energy. In which case do you increase the potential energy of the magnets? In which case do you increase the kinetic energy of the magnets?
Just like magnets, atoms of different elements are attracted together to form chemical bonds. Breaking these bonds requires energy. When a new bond forms, energy is released and temperatures rise. In the Reaction Energy Gizmo, you will explore how the energy of chemical bonding relates to temperature changes that occur during chemical reactions.
To begin, check that Reaction 1 and Forward are selected. In this reaction, hydrogen (H2) and oxygen (O2) react to form water (H2O). The reaction takes place inside a device called a calorimeter. Inside the calorimeter, a small chamber holds the reactants. The rest of the calorimeter is filled with water.
1. Click Play ( ). What happens?
2. How does the temperature change?
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Energy of chemical bonds Get the Gizmo ready:
● Check that Reaction 1 and Forward are selected.
● Select the INVESTIGATION tab.
Introduction: The heat energy stored in a chemical system is called the enthalpy (H) of the system. When atoms are joined by a chemical bond, energy must be added to pull them apart. This increases the enthalpy of the system. When a chemical bond forms, energy is released as shared electrons move into lower-energy orbitals. This causes the enthalpy to decrease.
Question: How can you predict how much energy is released in a chemical reaction?
1. Predict: In the warm-up activity, you observed how the reaction inside the chamber affected the temperature of the surrounding water. Based on what happens to the surrounding water, do you think heat energy (enthalpy) is absorbed in the reaction or released? Explain.
2. Observe: In the Gizmo, the energy required to break a chemical bond is modeled by placing a molecule into a set of mechanical claws. Place one of the hydrogen (H2) molecules between the claws, and press the Break bond.
A. What happens?
B. Look under the Energy absorbed column of the table. How much energy was required to break this bond?
Note: The energy is given here in units of kilojoules per mole (kJ/mol). This is the energy, in kilojoules, required to break all of the H–H bonds in one mole of H2 gas. [Show Less]