Energetics (TOPIC 16)

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

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

Overall change in energy DeltaH

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

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

Energy require to break bonds - Energy released

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

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

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.

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