9.2 - Measuring Enthalpy Change Flashcards Preview

OCR A Chemistry A Level - Chapter 9 > 9.2 - Measuring Enthalpy Change > Flashcards

Flashcards in 9.2 - Measuring Enthalpy Change Deck (4)
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What is the Kelvin scale?

degrees C +273 = K


What is the formula for finding energy?


q - heat energy in J
m - mass in g
delta T - change in temperature
c - specific heat capacity


Give the method for the experimental determination of enthalpy change of combustion.

1. Measure 150 cm3 of water and record the initial temperature
2. Add methanol to a spirit burner and weigh together
3. Light the burner as it heats the water
4. After 3 minutes record the water temperature as fire is extinguished
5. Re-weigh spirit burner
Use q=mc(delta)T
Then, do q/(mol of substance) = enthalpy change of combustion in kJ/mol


Why are there inaccuracies in the experimental value of enthalpy change of combustion?

- Heat loss to surrounding rather than water
- Incomplete methanol combustion
- Methanol may evaporate from wick, changing mass reading
- Non-standard conditions