Calorimetry 🔥 – Your Friendly Guide
1. What’s Happening?
In an isolated system no heat sneaks in or out. When some parts feel hotter than others, heat races from the hotter part to the cooler one until everyone settles at the same temperature 🧊. That simple race obeys a golden rule:
\( Q_{\text{lost (hot)}} = Q_{\text{gained (cold)}} \) :contentReference[oaicite:0]{index=0}
2. Meet the Calorimeter 🛠️
- A sturdy metallic vessel and a matching stirrer (usually copper or aluminium).
- The vessel hides inside a wooden jacket packed with insulating fluff like glass wool – this jacket blocks outside heat.
- A small opening lets a mercury thermometer peek in and track the temperature.
You drop hot and cold samples inside, close the lid, give the stirrer a friendly swirl, and let nature balance the heat 😎. :contentReference[oaicite:1]{index=1}
3. The Golden Formula ⚡
When two bodies share heat inside the calorimeter, the numbers line up as
\( m_1 s_1 (T_1 – T_f) = m_2 s_2 (T_f – T_2) \)
Here,
- \(m\) = mass of each body
- \(s\) = specific heat capacity
- \(T\) = temperature (with f for the final common value)
4. Walk-through Example 🧮
Find \(s_{Al}\) for an aluminium sphere.
- Sphere: \(m_1 = 0.047 \text{kg}\), heated to \(100^\circ\text{C}\).
- Calorimeter (copper): \(m_3 = 0.14 \text{kg}\), water inside: \(m_2 = 0.25 \text{kg}\) at \(20^\circ\text{C}\).
- Final mix temperature: \(23^\circ\text{C}\).
- Heat balance:
\(0.047\,s_{Al}\,(100-23)=\bigl(0.25\times4.18\times10^{3}+0.14\times0.386\times10^{3}\bigr)(23-20)\). - Solve ➡️ \(s_{Al}=0.911\,\text{kJ kg}^{-1}\text{K}^{-1}\).
Nice! 🎉
5. Handy Specific Heat Numbers 📊
| Substance | \(s\) (J kg-1 K-1) |
|---|---|
| Water 💧 | 4186 |
| Ice | 2060 |
| Aluminium | 900 |
| Copper | 386 |
| Iron | 450 |
Remember these – exam papers love them! :contentReference[oaicite:3]{index=3}
6. Why Water Is Special 💧✨
Water’s huge heat capacity makes it perfect:
- Coolant in car radiators.
- Hot-water bags for cozy warmth.
- Ocean breezes that keep coastal areas cooler in summer and milder in winter.
That giant number \(4186 \text{J kg}^{-1}\text{K}^{-1}\) shows why! :contentReference[oaicite:4]{index=4}
7. Molar Heat for Gases 🗒️
- Helium: \(C_p = 20.8\), \(C_v = 12.5\).
- Hydrogen: \(C_p = 28.8\), \(C_v = 20.4\).
- Nitrogen: \(C_p = 29.1\), \(C_v = 20.8\).
(Units: J mol-1 K-1) :contentReference[oaicite:5]{index=5}
8. High-Yield NEET Nuggets 🏆
- Principle of calorimetry: heat lost = heat gained – this forms the core of many numerical questions.
- Water’s specific heat: \(4186 \text{J kg}^{-1}\text{K}^{-1}\) – expect at least one direct or indirect question on this value.
- Calorimeter design: why insulation and a stirrer matter – conceptual MCQs love this detail.
- Example method: using the balance equation to find an unknown specific heat (like \(s_{Al}\)) – typical calculation pattern.
- Molar heat capacities: mono-atomic vs di-atomic gas values (e.g., helium vs nitrogen) – quick comparison questions.
You’ve got this! Keep practicing and watch those numbers add up 🚀
