9702 · 14.1
Thermal equilibrium flashcards
Revision flashcards for Cambridge 9702 Thermal equilibrium (syllabus 14.1). Flip, recall, then mark a real past-paper question.
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What defines thermal equilibrium between two objects?
No net transfer of thermal energy between them, resulting in a uniform temperature.
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State the Zeroth Law of Thermodynamics.
If object A and object B are each in thermal equilibrium with a third object C, then A and B are also in thermal equilibrium with each other.
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How do you convert a temperature reading from Celsius (°C) to Kelvin (K)?
Add 273.15 to the Celsius temperature: K = C + 273.15.
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What is the formula used to calculate the energy required to change the temperature of a substance?
Q = mcΔT, where Q is energy, m is mass, c is specific heat capacity, and ΔT is the temperature change.
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Why does the temperature of a substance remain constant during a phase change, even when heat energy is continuously added?
The added energy increases the potential energy of the particles by breaking or forming intermolecular bonds, rather than increasing their average kinetic energy.
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What is temperature a measure of?
The average kinetic energy of the particles within a substance.
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What is Absolute Zero?
The theoretical lowest possible temperature (0 K or -273.15 °C) where particles possess the minimum possible kinetic energy.
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Define internal energy.
The total sum of the random kinetic and potential energies of all the particles within a system.
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What is specific heat capacity (c)?
The energy needed to change the temperature of 1 kg of a substance by 1 K (or 1 °C) without a change of state. Units: J kg⁻¹ K⁻¹.
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What is specific latent heat (L)?
The energy required to change the state of 1 kg of a substance *without* changing its temperature. Units: J kg⁻¹.
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Why is the specific latent heat of vaporisation (Lᵥ) typically larger than fusion (Lₓ)?
More energy is required to completely separate particles into a gas (breaking almost all intermolecular bonds) than to merely loosen them in a liquid state.
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How does evaporation lead to cooling?
Higher-energy particles escape from the liquid surface, reducing the average kinetic energy and thus the temperature of the remaining liquid.
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What is the principle of conservation of energy in calorimetry problems?
Assuming no heat loss to the surroundings, the heat lost by hotter object(s) equals the heat gained by colder object(s).
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In an experiment to find specific heat capacity using an electrical heater, what quantities must be measured?
Mass of the substance (m), initial and final temperatures (to find ΔT), and the electrical energy supplied (E = VIt or from a joulemeter).
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How can heat loss to the surroundings be reduced in a calorimetry experiment?
By using an insulated container (e.g., a vacuum flask or lagged beaker), a lid to reduce convection and evaporation, and polishing surfaces to reduce radiation.
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What is the difference between internal energy and thermal energy (heat)?
Internal energy is the total energy (KE+PE) of particles *within* a system. Thermal energy (heat) is the energy *transferred* between systems due to a temperature difference.