4.1.1Additional lessons
Difference Between Heat and Temperature — IB Chemistry HL Revision Notes & Topical Questions
5 min read 5 parts Lesson 70 of 172
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Section 1 of 5Two Different Quantities
Temperature
- Temperature Temperature measures the average kinetic energy of the particles in a sample, and does not depend on the amount of substance.
Heat
- Heat Heat is energy transferred between objects because of a temperature difference, and it is measured in joules.
Direction
- Direction Energy always flows spontaneously from the hotter object to the cooler one until their temperatures are equal.
Extensive or intensive
- Extensive or intensive Heat content depends on the amount of substance, but temperature is the same for any amount in thermal equilibrium.
Example
- Example A bath of warm water holds far more thermal energy than a hot cup of tea even if the tea is at a higher temperature.
Section 2 of 5Measuring and Calculating
1
Temperature is measured in kelvin, where T(K) = θ(°C) + 273 (or 273.15 for more precise work).
2
A change of 1 K is the same size as a change of 1 °C, so ΔT can be used in either unit.
3
Specific heat capacity, c, is the energy needed to raise the temperature of 1 g of a substance by 1 K, and for water it is 4.18 J g⁻¹ K⁻¹.
4
The heat absorbed or released is q = mcΔT, with mass in grams, c in J g⁻¹ K⁻¹ and ΔT in K.
5
The sign of q shows whether energy is gained or lost, and the result is often converted to kJ.
| Quantity | Symbol | Unit |
|---|---|---|
| Heat | q | J or kJ |
| Mass | m | g |
| Specific heat capacity | c | J g⁻¹ K⁻¹ |
| Temperature change | ΔT | K or °C |
Section 3 of 5Particle View
Particle View
Kinetic energy
- Kinetic energy Hotter samples have particles moving faster on average, with a wide distribution of speeds.
Thermal equilibrium
- Thermal equilibrium No net heat flow occurs when two objects have equal temperatures.
Heat capacity
- Heat capacity Substances with strong intermolecular forces, such as water, require more energy per gram to heat.
Phase change
- Phase change During melting or boiling, heat is absorbed without a change in temperature because it is used to overcome forces.
Section 4 of 5Worked Example
Question
- Calculate the heat needed to warm 250 g of water from 20.0 °C to 45.0 °C.
- (c = 4.18 J g⁻¹ K⁻¹)
- ΔT = 45.0 − 20.0 = 25.0 K.
- q = mcΔT = 250 × 4.18 × 25.0.What the symbols mean: E, Q or q = energy transferred (J) · m = mass (kg; g in chemistry calorimetry) · c = specific heat capacity (J kg−1 °C−1; water 4.18 J g−1 °C−1) · ΔT or Δθ = temperature change (°C or K)
- q = 26 125 J.
- Convert to kJ26 125 ÷ 1000 = 26.1 kJ (3 s.f.).
Answer q ≈ 26.1 kJ
Section 5 of 5Exam Checklist & Tips
4.1.1 – Key Points for the Exam
- Temperature A measure of the average kinetic energy of the particles.
- Heat Energy transferred because of a temperature difference.
- Specific heat capacity Energy needed to raise 1 g of a substance by 1 K.
- Thermal equilibrium State in which there is no net heat flow between objects.
Common Mistakes
- Using heat and temperature as if they were the same thing.
- Using ΔT in kelvin with an extra 273 added when subtracting two Celsius values.
- Using mass in kilograms with c in J g⁻¹ K⁻¹.
- Assuming temperature must rise whenever heat is added, when it stays constant during a phase change.
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