2 (1.4) Enthalpy change

Question 1

Why may experimental value for enthalpy change be different to theoretical

Answer 1

-heat loss to apparatus/surroundings
-incomplete combustion of fuel
-evaporation of water/alcohol
-non- standard conditions

Question 2

Reduce uncertainty in mass measurement?

Answer 2

-use balance with greater resolution
-use larger mass

Question 3

Uncertainty calculation?

Answer 3

Uncertainty/calculated value x 100

Question 4

Accuracy?

Answer 4

How close experimental data is to accrual value

Question 5

How can experiment be more accurate?

Answer 5

-stir solution so temp evenly distributed
-use greater concentration- greater temp change- smaller uncertainty
-insulate by placing inside polystyrene cup & lid

Question 6

Describe a method of calorimetry

Answer 6

-Put polystyrene cup in beaker for insulation and support
-Measure out desired volumes of solutions with volumetric pipettes and transfer to insulated cup
-clamp thermometer into place
-Measure initial temperature of solution every 20s for 2 to 3 minutes
-At three minutes add reagent to cup and stir
-Record temp at regular intervals