Distinguishing Temperature from Heat

🟢 Lite — Quick Review (1h–1d)

Rapid summary for last-minute revision before your exam.

Temperature measures average kinetic energy of particles (K or °C); heat (kalor) is thermal energy transferred because of a temperature difference (joules). For a mass m of substance with specific heat c, the energy needed to change its temperature by ΔT is:

Q = m · c · ΔT (J)
Q = m · L for phase change, where L is latent heat (J/kg)
Azas Black: Q_released = Q_absorbed when substances reach thermal equilibrium.

Heat travels by conduction (Q/t = kAΔT/L), convection (mass motion of fluid), and radiation (H = σeAT⁴, remember Kelvin!). For UNDANA Saintek, expect 2–3 numerical items on azas Black or conduction.

🟡 Standard — Regular Study (2d–2mo)

Standard content for students with a few days to months.

Distinguishing Temperature from Heat

Suhu is an intensive state variable read by a thermometer (mercury, alkohol, termokopel). Kalor is extensive energy in transit. Two identical 50 °C copper blocks together are not “twice as hot” — they store twice the thermal energy at the same temperature.

Azas Black in Practice

When a hot object at T₁ is mixed with a cooler one at T₂ inside a calorimeter, the final temperature T is found from:

Σ m_i · c_i · (T_i − T) = 0 (sign convention: released = absorbed)

Always include the calorimeter’s heat capacity (C = m_cal · c_cal) when the problem says “bejana tembaga 100 g” — neglecting it is the single most common error in pencampuran questions.

Conduction Through a Slab

For steady-state conduction through a homogeneous wall of thickness L and area A:

Quantity	Symbol	Typical unit
Thermal conductivity	k	W/(m·K)
Cross-sectional area	A	m²
Thickness	L	m
Temperature difference	ΔT	K or °C

Rate H = Q/t = kA·ΔT/L. Materials with high k (copper ≈ 385, aluminium ≈ 205) are conductors; insulators like styrofoam have k ≈ 0.03.

Phase Change vs Temperature Change

On a heating curve, the flat regions correspond to melting or boiling — temperature is constant while latent heat L is absorbed. Distinguish kalor lebur (fusion) from kalor didih (vaporisation); for water L_fus = 3.34×10⁵ J/kg and L_vap = 2.26×10⁶ J/kg.

🔴 Extended — Deep Study (3mo+)

Comprehensive coverage for students on a longer study timeline.

Edge Cases in Azas Black

When ice at 0 °C is dropped into water, three stages may apply sequentially: (1) ice warms (if below 0 °C) using c_ice ≈ 2.09 kJ/(kg·K); (2) ice melts absorbing L_fus; (3) resulting water warms using c_water. Students often forget stage (1) and lose marks on sub-zero starting temperatures.

Radiation and the Kelvin Trap

Stefan–Boltzmann law H = σeAT⁴ requires absolute temperature. A common trap states “suhu permukaan 27 °C” — converting gives T = 300 K, so T⁴ = 8.1×10⁹. Forgetting the +273 yields an answer off by roughly 60%. Emissivity e ranges 0 ≤ e ≤ 1 (black body: e = 1).

Linear Expansion as a Heat Side-Effect

Although chiefly a mechanics topic, muai panjang (ΔL = αL₀ΔT) appears in compound soal UNDANA alongside conduction (e.g., bimetal strips in thermostats). Note α_steel ≈ 12×10⁻⁶ /°C, α_brass ≈ 19×10⁻⁶ /°C.

Common Mistakes

Confusing kapasitas kalor C (J/K, depends on mass) with kalor jenis c (J/(kg·K), an intensive property of the material). C = m·c.

Treating Q as a state variable instead of a path-dependent transfer.
Using °C inside T⁴ — always convert to Kelvin.
Sign errors when ΔT is negative (cooling).

Practice Prompts

A 200 g aluminium cup (c = 900 J/(kg·K)) holds 300 g of water at 20 °C. Steam at 100 °C (m_s = 20 g, L_vap = 2.26×10⁶ J/kg, c_water = 4200) is bubbled in. Find the final temperature, neglecting heat loss.
A glass window (k = 0.8 W/(m·K)) is 5 mm thick with area 2 m². Interior surface is 25 °C, exterior 5 °C. Compute the rate of conductive heat loss and discuss why double-glazing reduces it.

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Distinguishing Temperature from Heat