Enthalpy Change + Calorimetry Flashcards
What is the difference between endothermic and exothermic?
Endothermic: bringing energy in therefore POSITIVE VALUE
Exothermic: releasing energy out therefore NEGATIVE VALUE
What is enthalpy change (∆H)?
heat energy change at a constant pressure
What are the conditions for standard enthalpy?
100kPa, 298K
What is the definition of enthalpy of formation?
The enthalpy change when one mole of a substance is produced from its elements under standard conditions.
What is the definition of enthalpy of combustion?
The enthalpy change when one mole of a substance is burned completely in oxygen under standard conditions.
How do you calculate overall enthalpy change?
(∆H) = energy to break bonds (positive number) - energy to make bonds (negative number)
How to calculate the heat change (q)?
q = mc∆T
∆H=q/moles
m = mass
c = specific heat capacity
Why is the calculated bon enthalpy value differ from data book values?
data book values are an average.
What is calorimetry?
An experimental method for finding enthalpy change by measuring temperature over time.
Data can be extrapolated.
EQ: Describe how this data from the improved method can be used to
determine an accurate value for the temperature change.
EQ: What is the percentage uncertainty in the temperature change?
Answer: 7.7
Method:
0.1/2.6 x 2 x 100 = 7.7 (rounded)
EQ: which equation shows the enthalpy of combustion?
answer: A
EQ: Suggest how the students’ method, and the analysis of the results, could
be improved in order to determine a more accurate value for the enthalpy
of reaction.
EQ: A 50.0 g sample of water was used in this experiment.
Explain how you could measure out this mass of water without using a
balance.
- Water has a known density (of 1.0 g cm–3)
- Therefore, a volume of 50.0 cm3 could be measured out.
