Summary
Internal energy is the total of kinetic and potential energies within a system's molecules and varies with the phase of the substance. It is measured in Joules and influenced by temperature, molecular motion, and phase of matter.
- Internal Energy (U) — the sum of kinetic and potential energies within a system's molecules. Example: In a gas, internal energy is higher due to increased molecular motion.
- Kinetic Energy — energy due to the motion of molecules. Example: Heating a gas increases its kinetic energy, causing molecules to move faster.
- Potential Energy — energy stored due to the position of molecules. Example: In solids, potential energy is significant due to intermolecular forces.
- Ideal Gas — a theoretical gas with no intermolecular forces, having only kinetic energy. Example: An ideal gas's internal energy change is directly proportional to its temperature change.
Exam Tips
Key Definitions to Remember
- Internal energy is the sum of kinetic and potential energies within a system.
- Kinetic energy is the energy due to the motion of molecules.
- Potential energy is the energy stored due to the position of molecules.
Common Confusions
- Confusing internal energy with temperature; they are related but not the same.
- Assuming all gases behave as ideal gases; real gases have intermolecular forces.
Typical Exam Questions
- What happens to the internal energy of a gas when it is heated? The internal energy increases as kinetic energy increases.
- How does the phase of matter affect internal energy? Gases have higher internal energy compared to solids due to greater molecular motion.
- What is the relationship between internal energy and temperature in an ideal gas? Internal energy change is directly proportional to temperature change.
What Examiners Usually Test
- Understanding of how internal energy changes with temperature and phase.
- Ability to explain the relationship between kinetic energy and temperature.
- Knowledge of the differences between ideal and real gases.