Energetics (TOPIC 16)

Question 1

What is an exothermic reaction?

Answer 1

A reaction that gives out energy to the surroundings is usually in the form of heat and is usually shown by a rise in the temperature of the surroundings. Negative enthalpy change. Bonds made energy is released

Question 1

What is an endothermic reaction?

Answer 1

A reaction that takes in energy from the surroundings usually in the form of heat and is usually shown by a decrease in temperature of surroundings. Positive enthalpy change. Bonds broken so energy is required

Question 2

What is enthalpy change

Answer 2

Overall change in energy

DeltaH

Question 3

What does an exothermic energy profile diagram look like?

Answer 3

Products finisher lower than reactants because they are at a lower energy because energy is given out. Enthalpy change is negative.

Question 3

What does an endothermic energy profile diagram look like?

Answer 3

Reactant finish higher than products because they are at a higher energy because energy is taken in. Enthalpy change is positive

Question 3

Enthalpy change =

(Bonds)

Answer 3

Energy require to break bonds - Energy released

Question 4

Energy transferred =

Answer 4

mcdeltaT

m= mass of water in calorimeter
c = temp capacity
T = change in temp

Question 5

Calorimetry experiments to find out enthalpy change for displacement and dissolving

Talk about how to increase accuracy

Answer 5

Ensure reactants are all at the same temperature and mix in a polystyrene cup. Then measure the temperature change.

Biggest issue is energy loss so place polystyrene cup in a beaker of cotton wool to insulate.
Lid on top reduces energy lost through evaporation

Question 6

Calorimetry experiments to find out enthalpy change for neutralisation

Answer 6

Place 25cm^3 of an acid (HCl) and 25cm^3 of a base (sodium hydroxide) in separate test tubes.

Heat in a water bath to 25C

Add both to a polystyrene cup and mix.
Record the temperature every 30 seconds and record the highest temperature.

Question 7

Calorimetry experiments to find out enthalpy change for combustion

Answer 7

50g of water in a copper can - Good Conductor of heat - and record temperature.

Surround by draught excluder to reduce energy lost

Weight spirit burner and lid

Place the spirit burner underneath the can and light the wick

Stir the water constantly until the water reaches 50C and then cap the burner.

Weigh the spirit burner and lid again.

Calculate energy transferred using Q=MC∆T

Then to find energy produced by 1g of substance Q/Change in mass of burner