Energetics - 5.2

Question 1

What is meant by the term enthalpy changes?

Answer 1

The enthalpy change of a reaction is the heat energy releases or absorbs per mole.

Question 2

How does the sign tell us whether the reaction absorbs or releases energy?

Answer 2

positive – absorbed/endothermic.
Negative released/exothermic

Question 3

what is the equation for enthalpy change in a reaction?

Answer 3

Enthalpy change = bonds broken - bonds made

Question 4

what is a reaction profile diagram?

Answer 4

A reaction profile diagram is like an energy level diagram, but it shows the path the reaction actually takes from reactants to products

Question 5

What are the two formula used to convert our measurements into enthalpy change?

Answer 5

Q = mc🔺T

🔺H = -Q/moles

Question 6

what are the two significant sources of error in the combustion calorimetry experiment?

Answer 6

Heat loss – most of the heat energy dissipates into the air instead of the water.
Incomplete combustion this releases less heat energy than expected

Question 7

what are the sources of error in the solution calorimetry experiment?

Answer 7

heat loss and incomplete reaction like in combustion calorimetry
The water being heated is no longer pure water. This means that the specific heat capacity is no longer exactly 4.18 J/gram/° C.

Question 8

why would a polystyrene cup be used instead of a beaker?

Answer 8

Polystyrene cup is a good insulator therefore little energy is lost or gained

Question 9

What is meant by the term exothermic?

Answer 9

chemical reactions in which heat energy is given out

Question 10

What is meant by the term endothermic?

Answer 10

chemical reactions in which heat energy is taken in

Question 11

describe combustion calorimetry experiment

Answer 11

1. Weigh out 50 g of water and place in a can above the burner.
2. Measure the initial mass of the burner and the initial
   temperature of the water.
3. Ignite the burner, stir water for 30 seconds, then extinguish
   the burner.
4. Measure the final mass of the burner and the final (maximum)
   temperature of the water.

Question 12

describe solution calorimetry experiment

Answer 12

1. Pipette 25 cm3 of CuSO4(aq) into a polystyrene cup. 1 cm3
   solution has a mass of 1 g
2. Measure the initial temperature of the solution.
3. Add 1 g of Mg(s) and stir continuously.
4. Measure the maximum temperature of the solution.