AS 91390 · 5 credits · External
Thermochemical principles
Demonstrate understanding of thermochemical principles and the properties of particles and substances
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In plain EnglishAI study guide · check the NZQA standard
You need to show you understand how and why chemical reactions happen by explaining the particles involved, the energy changes, and the forces between molecules. This standard asks you to link ideas about entropy, heat energy, intermolecular forces, and periodic trends to explain real chemical behaviour rather than just recalling facts.
What to do, grades and common mistakes
What you actually do
- ·Draw and label Lewis structures of molecules and explain their shapes using electron density regions
- ·Explain the polarity of molecules and justify differences in bond angles between similar molecules
- ·Use entropy changes in the system and surroundings to explain why reactions happen spontaneously
- ·Describe and compare the strength of intermolecular forces (temporary dipoles, hydrogen bonds) and link this to particle properties like electron cloud size
- ·Calculate enthalpy changes using Hess' Law and relate periodic trends (ionisation energy, atomic radius, ionic radius) to nuclear charge, electron shielding, and energy levels
AAchieved
You draw Lewis structures and name molecular shapes correctly, identify entropy changes, write electron configurations properly, and recognise that intermolecular forces exist between molecules rather than within them.
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