The chemical properties of the halogen elements and the hydrogen halides
Cambridge A-Level Chemistry (9701) · Unit 11: Group 17 · 7 flashcards
The chemical properties of the halogen elements and the hydrogen halides is topic 11.2 in the Cambridge A-Level Chemistry (9701) syllabus , positioned in Unit 11 — Group 17 , alongside Some reactions of the halide ions and The reactions of chlorine. In one line: H₂(g) + Cl₂(g) → 2HCl(g). This reaction requires UV light or heat to overcome the high activation energy.
Marked as AS Level: examined at AS Level in Paper 1 (Multiple Choice), Paper 2 (AS Structured Questions) and Paper 3 (Advanced Practical Skills). The same content may also be assumed in Paper 4 (A Level Structured Questions).
The deck below contains 7 flashcards — 2 definitions and 5 key concepts — covering the precise wording mark schemes reward. Use the 2 definition cards to lock down command-word answers (define, state), then move on to the concept and calculation cards to handle explain, describe, calculate and compare questions.
Write a balanced chemical equation for the reaction between chlorine and hydrogen
H₂(g) + Cl₂(g) → 2HCl(g). This reaction requires UV light or heat to overcome the high activation energy.
What the Cambridge 9701 syllabus says
Official 2025-2027 spec · AS LevelThese are the exact learning outcomes Cambridge sets for this topic. The candidate is expected to be able to do each of these on the relevant paper.
- describe the relative reactivity of the elements as oxidising agents
- describe the reactions of the elements with hydrogen and explain their relative reactivity in these reactions
- describe the relative thermal stabilities of the hydrogen halides and explain these in terms of bond strengths
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 9701 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Tips to avoid common mistakes in The chemical properties of the halogen elements and the hydrogen halides
- › Memorize the balanced equation for the decomposition of Group 2 nitrates: 2M(NO3)2 → 2MO + 4NO2 + O2.
- › Practice balancing equations for the thermal decomposition of Group 2 nitrates, ensuring the 2:2:4:1 molar ratio is maintained.
- › Distinguish between reactions that produce gas (like metals with acid) and those that simply dissolve to form a solution.
- › Apply the specific equation: 3Cl2 + 6NaOH → 5NaCl + NaClO3 + 3H2O to determine the correct molar yield of products.
- › Write out the full balanced equation for precipitation: Al2Cl6 + 6NaOH → 2Al(OH)3 + 6NaCl to find the correct molar ratio y/x.
Describe the trend in oxidising ability of the halogens down Group 17.
Oxidising ability decreases down the group. This is because atomic radius increases, shielding increases, and nuclear attraction decreases, making it harder to attract an electron to form a negative ion.
Write a balanced chemical equation for the reaction between chlorine and hydrogen.
H₂(g) + Cl₂(g) → 2HCl(g). This reaction requires UV light or heat to overcome the high activation energy.
Explain the relative reactivity of halogens with hydrogen down Group 17.
Reactivity decreases down the group. This is due to the decreasing bond enthalpy of the H-X bond (X = halogen), making it harder to break the bond and form the hydrogen halide.
Describe the trend in thermal stability of the hydrogen halides (HX) down Group 17.
Thermal stability decreases down the group. This is because the bond enthalpy of the H-X bond decreases as you go down the group, making it easier to break the bond upon heating.
Explain the relationship between H-X bond strength and the thermal stability of hydrogen halides.
Stronger H-X bonds require more energy to break, resulting in higher thermal stability. Conversely, weaker H-X bonds break more easily, leading to lower thermal stability.
Arrange the hydrogen halides (HF, HCl, HBr, HI) in order of increasing thermal stability.
HI < HBr < HCl < HF. This is because the H-F bond is the strongest and the H-I bond is the weakest.
Why does fluorine react more vigorously with hydrogen than iodine does?
Fluorine reacts more vigorously with hydrogen than iodine because the F-F bond is weaker than the I-I bond, and the H-F bond formed is stronger than the H-I bond. These differences require less energy to react.
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The chemical properties of the halogen elements and the hydrogen halides sits alongside these A-Level Chemistry decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.
Key terms covered in this The chemical properties of the halogen elements and the hydrogen halides deck
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