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8. Calcium carbonate reacts with dilute hydrochloric acid to produce calcium chloride, water and carbon dioxide - Edexcel - GCSE Chemistry - Question 8 - 2019 - Paper 1
Question 8
8. Calcium carbonate reacts with dilute hydrochloric acid to produce calcium chloride, water and carbon dioxide. CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂ (a) A student wan... show full transcript
Worked Solution & Example Answer:8. Calcium carbonate reacts with dilute hydrochloric acid to produce calcium chloride, water and carbon dioxide - Edexcel - GCSE Chemistry - Question 8 - 2019 - Paper 1
Step 1
Complete Figure 4 to show the apparatus that could be used to measure accurately the volume of gas given off in two minutes.
Answer
To accurately measure the volume of gas produced in this reaction, it is essential to use a gas syringe or an inverted measuring cylinder filled with water. The apparatus should include the following elements:
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Delivery Tube: Connect a delivery tube from the conical flask where the reaction occurs to the gas syringe or the inverted measuring cylinder. Ensure that the delivery tube is not submerged in liquid, and attach it securely to avoid any gas leaks. A bung (cork) can be used to seal the flask.
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Gas Syringe: Use a gas syringe to accurately collect the gas as it is produced. Ensure it is calibrated properly to measure the volume of gas accurately.
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Inverted Measuring Cylinder: Alternatively, an inverted measuring cylinder can be used, placed upside down in a basin of water, to capture the gas released from the flask. The volume of gas can be measured by observing the water displacement.
This setup allows for the precise measurement of the gas volume produced over the two-minute interval.
Step 2
Explain, in terms of bond breaking and bond making, why some reactions are exothermic.
Answer
The reaction between calcium carbonate and dilute hydrochloric acid is exothermic, meaning it releases heat into the surroundings. This can be explained through the concepts of bond breaking and bond making:
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Breaking Bonds: During the reaction, energy is initially required to break the bonds in the reactants, calcium carbonate (CaCO₃) and hydrochloric acid (HCl). This process is endothermic as it absorbs energy.
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Making Bonds: As new products — calcium chloride (CaCl₂), water (H₂O), and carbon dioxide (CO₂) — are formed, new bonds are created. This bond formation releases energy into the environment, which more than compensates for the energy absorbed in the bond-breaking stage.
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Net Energy Change: For a reaction to be classified as exothermic, the total energy released during the formation of the products must be greater than the energy consumed to break the bonds of the reactants. Therefore, in this reaction, the energy released in making the new bonds results in a net release of energy, explaining why the reaction is exothermic.
In summary, exothermic reactions occur when the energy released from forming new bonds exceeds the energy needed to break the old bonds.