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4.1.1Additional lessons

Difference Between Heat and Temperature — IB Chemistry SL Revision Notes & Topical Questions

5 min read 6 parts Lesson 48 of 98

📚 IB Chemistry SL Hub / Topical Revision
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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.
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Part 1 of 6Two Different Quantities

A cup of tea and a bath of warm water make the difference clear.

Temperature
  • Temperature A measure of the average kinetic energy of the particles in a substance;
    • it does not depend on how much of the substance is present.
Heat
  • Heat Thermal energy that flows from a hotter object to a colder one because of a temperature difference between them.
Total energy
  • Total energy The thermal energy stored in a sample depends on both its temperature and its mass, so a large sample holds more than a small one.
Direction of flow
  • Direction of flow Energy transfers spontaneously from the higher temperature region to the lower one until both are at the same temperature.
PropertyTemperatureHeat
MeasuresAverage kinetic energy of particlesEnergy transferred or stored as thermal energy
UnitK or °CJ or kJ
Depends on amount of substance?NoYes

Part 2 of 6Units and Scales

Units and Scales
Kelvin scale
  • Kelvin scale The kelvin is the SI unit of temperature, and 0 K is absolute zero, where particles would have minimum kinetic energy.
Conversion
  • Conversion Temperature in kelvin equals temperature in °C plus 273, so 25 °C is 298 K on the data booklet scale.
Temperature change
  • Temperature change A change of 1 °C is the same size as a change of 1 K, so ΔT can be recorded on either scale without converting.
Energy units
  • Energy units Heat is measured in joules, and one kilojoule equals 1000 joules, so a value in J is divided by 1000 to give kJ.

Part 3 of 6Particles and Energy

Heat transfer can be followed at the level of particle collisions.

1
Particles in a hot sample move, vibrate and rotate faster than those in a cold sample, so their average kinetic energy is greater.
2
When a hot and a cold object touch, collisions between particles at the boundary pass kinetic energy from fast particles to slow ones.
3
The hot object cools as its particles lose energy while the cold object warms as its particles gain energy.
4
Transfer continues until thermal equilibrium is reached, when both objects have the same temperature and there is no net flow of heat.

Part 4 of 6Energy in Chemical Systems

Energy in Chemical Systems
Conservation of energy
  • Conservation of energy Energy cannot be created or destroyed, only transferred between the system and the surroundings or changed into another form.
System
  • System The chemical reaction mixture being studied, whereas everything else, including the container and the air, is the surroundings.
Heat capacity idea
  • Heat capacity idea Different amounts of heat are needed to raise the temperature of equal masses of different substances by the same amount.
Link to enthalpy
  • Link to enthalpy Measuring a temperature change in the surroundings allows the heat released or absorbed by a reaction to be calculated.

Part 5 of 6Worked Example

Question

  • Compare the heat needed to warm 250 g and 1.0 g of water from 20 °C to 80 °C.
  • Use c = 4.18 J g⁻¹ K⁻¹.

  1. The temperature change is 80 − 20 = 60 °C, which is 60 K.
  2. For 250 g: Q = mcΔT = 250 × 4.18 × 60 = 62 700 J = 62.7 kJ.
    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)
  3. For 1.0 g: Q = 1.0 × 4.18 × 60 = 251 J (3 s.f.).
  4. Both samples reach the same final temperature but need very different amounts of heat.

Answer 250 g needs 62.7 kJ and 1.0 g needs about 0.25 kJ, so heat depends on amount but temperature does not.

Part 6 of 6Exam Checklist & Tips

4.1.1 – Key Points for the Exam

  • Temperature A measure of the average kinetic energy of the particles in a sample.
  • Heat Energy transferred between a system and its surroundings because of a temperature difference.
  • Kelvin
    • The SI unit of temperature;
      • T(K) = T(°C) + 273.
  • Thermal equilibrium The state in which two objects in contact have the same temperature and no net heat flows.
  • Joule The SI unit of energy, with 1 kJ equal to 1000 J.

Common Mistakes

  • Saying a high temperature always means a large amount of heat, when a small hot sample can hold less energy than a large cooler one.
  • Adding 273 to a temperature change, when a change in °C is numerically equal to the change in K.
  • Forgetting to convert joules to kilojoules before giving an enthalpy change in kJ mol⁻¹.
  • Describing heat as something an object contains rather than as energy being transferred.

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