9702 · 16.1
Internal energy flashcards
Revision flashcards for Cambridge 9702 Internal energy (syllabus 16.1). Flip, recall, then mark a real past-paper question.
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What makes up a system's internal energy?
The total random kinetic and potential energies of all its constituent particles.
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How does temperature affect a system's internal energy?
Higher temperature means higher average kinetic energy of particles, thereby increasing internal energy.
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State the First Law of Thermodynamics.
$\Delta U = Q + W$ (Change in internal energy = Heat added to system + Work done on system).
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What does a negative 'Q' value mean in $\Delta U = Q + W$?
Heat energy is transferred *out of* the system (e.g., the system cools down).
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When is 'W' (work done) negative in the First Law?
When work is done *by* the system (e.g., an expanding gas pushes a piston).
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Is internal energy considered a 'state function'?
Yes, it depends only on the system's current physical state (e.g., temperature, pressure, volume), not how it got there.
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Name two ways to increase a system's internal energy.
By doing work *on* the system or by transferring energy *to* it via heating.
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What does a positive $\Delta U$ signify?
An increase in the system's total internal energy.
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Why is internal energy considered to involve 'random' energies?
Because the motion and positions of individual particles are unpredictable, disordered, and chaotic.
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For an ideal gas, what is the internal energy solely dependent on?
Its absolute temperature. Since there are no intermolecular forces, potential energy is zero, so internal energy is just the total random kinetic energy of the molecules.