temperature and heat Flashcards
What is temperature in physics?
Temperature (T) is a measure of the average kinetic energy of the atoms or molecules in a substance, indicating its physical state.
How does heat differ from temperature?
Heat (Q) is energy that flows between objects due to a temperature difference, while temperature is a measure of an object’s internal energy state. Objects don’t “contain” heat, but heat flows into or out of them.
What is thermal equilibrium?
Thermal equilibrium occurs when two objects in contact reach the same temperature, and no net heat flows between them. It’s the basis of the 0th Law of Thermodynamics
How do you convert Celsius to Kelvin?
K = C + 273
What is absolute zero?
Absolute zero is 0 K (-273.15°C), the temperature at which a gas would exert no pressure and particles have minimal energy, though quantum effects still cause motion.
What is the formula for linear thermal expansion?
ΔL=αL0ΔT
L = L0(1+αΔT)
ΔL is the change in length,
α is the coefficient of linear expansion(K^-1),
L0 is the initial length, and
ΔT is the temperature change.
Volume expansion formulas?
ΔV=βV0ΔT
V = V0(1+ βΔT)
β=3α,
β is the coefficient of volume expansion(K^-1)(kalvin),
V0 is the initial volume, and
ΔT is the temperature change.
What happens to the size of a hole in a plate when the temperature increases?
The hole becomes larger because the entire plate, including the hole, expands uniformly with temperature increase (linear thermal expansion applies to all dimensions).
Wat is heat?
energy that is flowing from one body to another due to a temperature difference.
What is heat flow?
energy transfer that takes place solely because of a temperature difference
What is specific heat?
Specific heat (c) is the amount of heat (in J) needed to raise the temperature of 1 kg of a material by 1 K, with units J/kg·K.
Formula:
Q=mcΔT.
What is molar heat capacity?
Molar heat capacity (C) is the heat needed to raise the temperature of 1 mole of a substance by 1 K, with units J/mol·K. It relates to specific heat by
C=Mc, where
M is the molar mass.
What is the heat of fusion?
It is the heat per unit mass required to change a substance from solid to liquid at its melting point, with
Q=+mLf
for melting.
What is the heat of vaporization?
The heat of vaporization is the heat per unit mass required to change a substance from liquid to gas at its boiling point, with
Q=+mLv
for vaporization.
Name the three mechanisms of heat transfer.
Conduction, convection, and radiation.
What is thermal conductivity?
Thermal conductivity (k) measures a material’s ability to conduct heat.
The heat current is given by
H = k * A * ((T_H - T_C) / L)
where A is the area,
T_H - T_C is the temperature difference L is the length.
What is blackbody radiation?
Blackbody radiation is electromagnetic radiation emitted by an object due to its temperature (above 0 K).
It’s described by the Stefan-Boltzmann Law:
H = sigma * e * A * T^4,
where sigma is a constant,
e is emissivity,
A is area, and
T^4 is temperature to the fourth power.
How does water’s anomalous expansion affect lakes?
Water’s density decreases from 4°C to 0°C, causing it to expand and float as ice. This makes lakes freeze from the top down, allowing life to survive below the ice.
What is the greenhouse effect’s role in climate change?
The greenhouse effect traps infrared radiation in the atmosphere due to gases like CO2, increasing global temperatures. It’s essential for life but enhanced by human activity.
What does Sum Q = 0 represent in calorimetry?
In an isolated system, the sum of all heat flows (into and out of objects) equals zero, written as Sum Q = 0, reflecting conservation of energy
What is a thermal conductor?
A thermal conductor is a material that allows heat to flow easily through it, facilitating energy transfer between objects
What is a thermal insulator?
A thermal insulator is a material that prevents or slows the flow of heat, impeding energy transfer between objects
How do thermometers measure temperature?
Thermometers measure temperature indirectly by detecting changes caused by heat, such as liquid volume expansion, gas pressure changes, or bending of a bimetallic strip.
What is the molecular model for thermal expansion?
In solids, atoms are held by interatomic forces (like springs). As temperature rises, larger vibration amplitudes increase the average distance between atoms, causing expansion
What is the heat of sublimation?
The heat of sublimation (L_s) is the heat per unit mass needed to change a substance directly from solid to gas, with Q = +m * L_s for sublimation.
What is the heat of combustion?
The heat of combustion (L_c) is the heat released per unit mass when a substance burns, with Q = -m * L_c (e.g., petrol: 4.6 * 10^7 J/kg).
What is a mole and Avogadro’s number?
A mole is the amount of substance containing 6.022 * 10^23 entities (Avogadro’s number, N_A). Mass relates to moles by m = n * M, where M is molar mass.
How is absolute zero determined experimentally?
Absolute zero (0 K) is the temperature where a gas’s pressure extrapolates to zero in a constant-volume gas thermometer, indicating minimal particle energy.
What is thermal stress?
Thermal stress is the internal stress in a material caused by temperature changes when expansion or contraction is constrained.
What types of radiation are emitted by a blackbody?
A blackbody emits radiation depending on its temperature, including ultraviolet, visible, infrared, or far infrared light.
What is phase equilibrium?
Phase equilibrium is the condition during a phase change where both phases (e.g., solid and liquid) coexist at the same temperature and pressure.
The equilibrium which exists between or within
different states of matter, namely solid, liquid and gas.
How is the Kelvin scale related to gas pressure?
In the Kelvin scale, the ratio of two temperatures T_1 / T_2 equals the ratio of the corresponding gas-thermometer pressures p_1 / p_2.
Is a temperature change (ΔT) different in Celsius and Kelvin?
No, a temperature change (ΔT) is the same in Celsius and Kelvin because both scales have the same size degree, only differing by a constant offset.
When are thermal expansion equations valid?
The simplified thermal expansion equations (ΔL = α L_0 ΔT, ΔV = β V_0 ΔT) are valid when α * ΔT is much less than 1, ensuring small changes.
What makes convection different from conduction?
Convection is a heat transfer process that involves the physical movement of mass (e.g., fluid motion), unlike conduction, which occurs without bulk motion.
What is the full statement of the 0th Law of Thermodynamics?
If system A is in thermal equilibrium with system C, and system B is also in thermal equilibrium with system C, then A and B are in thermal equilibrium with each other.
When do you use Q = m c ΔT versus Q = ± m L in heat calculations?
Use Q = m c ΔT when heat changes an object’s temperature within one phase (e.g., warming water). Use Q = ± m L when heat causes a phase change at a constant temperature (e.g., melting ice or boiling water), with + for heat added and - for heat released.
How do thermal resistance and thermal conductivity differ, when can you sum them, and which do you use in calculations?
Thermal conductivity (k) measures how well a material conducts heat, used in H = k * A * (T_H - T_C) / L for a single material’s heat current. Thermal resistance (R = L / (k * A)) measures how much a material resists heat flow, used as H = (T_H - T_C) / R. Sum R values when heat flows through multiple layers in series (e.g., wall insulation). Use k for material properties; use R for total resistance in layered systems.
conductivity
The ability of an object or substance to let electricity
or heat flow through it
convection
The transfer of heat by the spontaneous motion of
liquid or gas when temperature differences exist between different positions inside a volume of the liquid or gas.
OR
transfer of heat by the mass motion of fluid.
equilibrium
A condition of a system when the state and
properties of the system (its motion, its
temperature, pressure, etc.) all stay constant over
time.
heat current
The rate of heat flow from a body with a higher
temperature to a body with a lower temperature.
insulator
A material that does not easily allow electricity, heat
or sound to pass through it.
phase change
The process for a substance to change from one
phase to another phase, for example from solid to
liquid.
phase shift
A change of the phase angle of a sinusoidal
function.
thermal conductivity
The ability of a substance to let heat flow through it
thermal equilibrium
The condition under which two substances in
physical contact with each other are at the same
temperature, and therefore no net heat exhange
takes place between them
thermal expansion
The increase of the size of a solid object when its
temperature is increased.
thermal resistance
The ability of a slab of material of a particular
thickness to oppose the flow of heat through it
Heat current equations
H = ΔQ/Δt
H = kA(T_hot - T_cold)/L
R = L/k
H = A(T_hot - T_cold)/R
R - thermal resistance(layers can be added to get R_total)
H - heat current
k - thermal conductivity(w/m.K)
A - cross sectional area
L -length(how far heat must flow)
forced convection
takes place when fluid is circulated by a pump
free convection
caused by differences in density due to thermal expansion
Radiation
transfer of heat by electromagnetic waves, such as infrared, visible and UV light.
Stefan Boltzmann law
heat current radiated out by a body with temperature T in KALVIN!!!! is:
H = AeoT^4
A - surface area
T - temperature in kalvin
e - emissivity of object
o - constant
a body radiates + absorbs radiation emitted by its surroundings:
Hnet = AeoT^4 - AeoT^4_surroundings
Avogadro’s number
Definition: One mole of a substance contains as many elementary
entities (atoms or molecules) as there are atoms in 12 g of carbon-12.
