Name: Date:
Lab 22: Student Exploration: Reaction Energy
Directions: Follow the instructions to go through the simulation. Respond to the questions 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?
Pull them apart
2. Suppose you held two magnets a short distance apart, then let go. What would happen?
Depends on which poles of the magnets were facing each other. If one was positive and
one was negative, they would be attracted to each other. If they were either both
positive or negative, they would repel.
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?
Kinetic energy increases if you were to move magnets with the same charge towards
each other because they are going to repel. Potential energy would increase if they
were different poles because they are attracted to each other.
Gizmo Warm-up
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?
Temperature increases, moving molecules.
2. How does the temperature change?
Increases
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Activity A:
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.
Heat is released because the surrounding water is absorbing the heat (which we know
because the temperature increases).
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? The bond between the atoms is broken and energy is absorbed.
B. Look under the Energy absorbed column of the table. How much energy was required to break this
bond?
436kJ/mol
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.
C. Remove the hydrogen atoms from the claws and then break apart the other H–H molecule.
What is the total energy absorbed so far? 872kJ/mol
3. Measure: Notice that the oxygen atoms are connected by a double covalent bond. This is because the
oxygen atoms share two pairs of electrons. Place the oxygen molecule in the claws and press the Break
bond.
A. How much energy is required to break the first O–O bond? 349kJ/mol
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