ALEX Classroom Resource

Developing and Using Models; Planning and Carrying out Investigations; Constructing Explanations and Designing Solutions

Crosscutting Concepts: Cause and Effect; Systems and System Models; Stability and Change

Disciplinary Core Idea: Energy

Students:

• Explain how the release or absorption of energy from a system depends on changes that occur in the components of the system.
• Develop a model to illustrate how changes in total bond energy determine if a chemical reaction is endothermic or exothermic.
• Plan an investigation and in the design decide on types, how much, and accuracy of data needed to produce reliable measurements.
• Evaluate the investigation design to consider limitations on the precision of the data (e.g., number of trials, cost, risk, time) and to identify potential causes of apparent loss of energy from a closed system.
• Conduct investigation as designed and if necessary, refine the plan to produce more accurate, precise, and useful data.
• Use evidence from investigation to support the idea that the transfer of thermal energy when two components of different temperature are combined within a closed system results in a more uniform energy distribution among the components in the system.

Students know:

• Energy is a quantitative property of a system that depends on the motion and interactions of matter and radiation within that system. That there is a single quantity called energy is due to the fact that a system's total energy is conserved, even as within the system, energy is continually transferred from one object to another and between its various possible forms.
• Models are developed based on evidence to illustrate the relationships between systems or between components of a system.
• A stable molecule has less energy than the same set of atoms separated; one must provide at least this energy in order to take the molecule apart.
• In chemical processes, whether or not energy is stored or released can be understood in terms of collisions of molecules and rearrangement of atoms into new molecules.
• The energy change within a system is accounted for by the change in the bond energies of the reactants and products.
• Breaking bonds requires an input of energy from the system or surroundings, and forming bonds releases energy to the system and surroundings.
• The energy transfer between systems and surroundings is the difference in energy between bond energies of the reactants and products.
• Although energy cannot be destroyed, it can be converted to less useful forms (i.e., to thermal energy in the surrounding environment).
• The overall energy of the system and surroundings is conserved during the reaction.
• Energy transfer occurs during molecular collisions.

Students are able to:

• Construct and revise an explanation based on valid and reliable evidence obtained from a variety of sources (students' own investigations, models, theories, simulations, peer review) and the assumption that theories and laws that describe the natrual world operate today as they did in the past and will continue to do so in the future.
• Apply scientific principles and evidence to provide an explanation of phenomena.
• Develop a model based on evidence to illustrate the relationships between systems or components of a system.
• Describe relationships between system components to illustrate that the net energy change within the system is due to bonds being broken and formed, that the energy transfer between the system and surroundings results from molecular collisions, and that the total energy change of the chemical reaction system is matched by an equal but opposite change of energy in the surroundings.
• Plan an investigation that describes experimental procedure (including safety considerations), how data will be collected, number of trials, experimental setup, equipment required, and how the closed system will be constructed and initial conditions of system.
• Conduct an investigation to collect and record data that can be used to calculate the change in thermal energy of each of the two components of the system.

Students understand that:

• Energy is a quantitative property of a system that depends on the motion and interactions of matter and radiation within that system. That there is a single quantity called energy is due to the fact that a system's total energy is conserved, even as within the system, energy is continually transferred from one object to another and between its various possible forms.
• When investigating or describing a system, the boundaries and initial conditions of the system need to be defined and their inputs and outputs analyzed and described using models.
• Models are developed based on evidence to illustrate the relationships between systems or between components of a system.
• A stable molecule has less energy than the same set of atoms separated; one must provide at least this energy in order to take the molecule apart.
• In chemical processes, whether or not energy is stored or released can be understood in terms of collisions of molecules and rearrangement of atoms into new molecules.
• Uncontrolled systems always evolve toward more stable states (i.e., toward more uniform energy distribution).
• The distribution of thermal energy is more uniform after the interaction of the hot and cold components.
• Energy cannot be created or destroyed, but it can be trasported from one place to another and transferred between systems.
• Scientists plan and conduct an investigation individually and collaboratively to produce data to serve as the basis for evidence and in the design, decide on types, how much, and accuracy of data needed to produce reliable measurements and consider limitations on the precision of data. Uncontrolled systems always evolve toward more stable states (i.e., toward more uniform energy distribution).
• The distribution of thermal energy is more uniform after the interaction of the hot and cold components.
• Energy cannot be created or destroyed, but it can be trasported from one place to another and transferred between systems.
• When investigating or describing a system, the boundaries and initial conditions of the system need to be defined and their inputs and outputs analyzed and described using models.

ASIM Module:
This standard does not include calculating the total bond energy changes during a chemical reaction from the bond energies of reactants and products. 11b. Emphasis is on analyzing data from student investigations and using mathematical thinking to describe energy changes both quantitatively and conceptually. Examples could include mixing liquids at different initial temperatures or adding objects at different temperatures to water. Heat capacity values of components in the system should be obtained from scientific literature. Endothermic and Exothermic Reactions; Energy Content of Food; Hess's Law; Particle Collisions and Activation Energy; Excited electrons; Energy Changes in Simple Distillation; Elephant Toothpaste; Specific Heat