Thermal decomposition
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レッスンノート
What is Thermal Decomposition?
- Thermal decomposition is a chemical reaction where a compound is heated and breaks down into smaller, simpler products.
- It requires heat energy to break the chemical bonds in the compound.
Example: Copper Carbonate
- Heating copper carbonate (green) produces copper oxide (black) and carbon dioxide gas.
- Word equation: copper carbonate → copper oxide + carbon dioxide.
- Symbol equation: CuCO₃ → CuO + CO₂.
- The colour change from green to black is evidence of a chemical reaction.
- The release of carbon dioxide gas is another sign of reaction.
General Rule for Metal Carbonates
- When heated, a metal carbonate generally decomposes into a metal oxide and carbon dioxide.
- Example: magnesium carbonate → magnesium oxide + carbon dioxide (MgCO₃ → MgO + CO₂).
- Example: calcium carbonate → calcium oxide + carbon dioxide (CaCO₃ → CaO + CO₂).
Testing for Carbon Dioxide
- Carbon dioxide gas turns limewater (calcium hydroxide solution) milky/cloudy white.
- This is a positive test for carbon dioxide.
Example: Hydrogen Peroxide
- Hydrogen peroxide decomposes into water and oxygen gas when heated.
- Word equation: hydrogen peroxide → water + oxygen.
- Balanced symbol equation: 2H₂O₂ → 2H₂O + O₂.
Testing for Oxygen
- Oxygen gas will relight a glowing splint.
- This is a positive test for oxygen.
Balancing Equations
- Example: Silver oxide decomposes: 2Ag₂O → 4Ag + O₂ (balanced).
- Always ensure the number of atoms of each element is equal on both sides.
Particle arrangement in solids, liquids, and gases. Thermal decomposition involves breaking bonds, often producing gases.
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練習問題
無料プレビュー — 56問中8問。すべて見るには登録を。
1.What is thermal decomposition?
Easy- AA reaction where a compound is heated and breaks down into simpler products
- BA reaction where two elements combine to form a compound
- CA reaction where a substance burns in oxygen
- DA reaction where a compound is broken down by electricity
2.When copper carbonate undergoes thermal decomposition, what are the products?
Easy- ACopper oxide and carbon dioxide
- BCopper and carbon dioxide
- CCopper oxide and oxygen
- DCopper and oxygen
3.What colour change occurs when copper carbonate is heated?
Easy- AFrom green to black
- BFrom black to green
- CFrom green to white
- DFrom white to black
4.Which test is used to confirm that a gas is carbon dioxide?
Easy- ABubble the gas through limewater; it turns milky
- BHold a glowing splint near it; it relights
- CHold a lighted splint near it; it pops
- DCollect the gas in a test tube and smell it
5.Balance the equation: ___ Ag2O → ___ Ag + O2
Medium- A2 Ag2O → 4 Ag + O2
- BAg2O → 2 Ag + O2
- C2 Ag2O → 2 Ag + O2
- D3 Ag2O → 6 Ag + O2
6.Which of the following is a sign that a chemical reaction has occurred when heating copper carbonate?
Easy- AA colour change and gas release
- BOnly a colour change
- COnly gas release
- DNo change is observed
7.What is the balanced chemical equation for the thermal decomposition of hydrogen peroxide?
Medium- A2 H2O2 → 2 H2O + O2
- BH2O2 → H2O + O2
- C2 H2O2 → H2O + 2 O2
- DH2O2 → 2 H2O + O2
8.What is the test for oxygen gas?
Easy- AIt relights a glowing splint
- BIt turns limewater milky
- CIt burns with a squeaky pop
- DIt bleaches damp litmus paper
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