revision topic 11 Flashcards
what are exothermic reactions
they are reactions that transfer energy from the reacting chemical to their surrounding thus they heat up their surrounding and you can measure a temperature increase
whar are endothermic reactions
they are reactions that transfer energy from their surroundings to the reacting chemicals where we can measure the temperature drop
examples of exothermic and endothermic reactions
exothermic: burning fuels and neutralization reactions
endothermic: thermal decomposition
what is the enthalpy change
it is a term used to describe the transfer of energy in a chemical reaction that has constant pressure and has the symbol H, since in exothermic reactions the reactant has more enthalpy content than the products it would always be a negative number and because the products in endothermic reactions have more enthalpy than the reactant it would always be a positive number
explain how exothermic reactions can be used
they can be used in hand warmers which some are used more than once because of the crystallization of a supersaturated solution while some can be used only once and self-heating cans
explain how endothermic reactions can be used
they can be used in instant cold packs for sport injuries
explain how energy can work in reversible equations
if you make one side of a chemical equation exothermic the other side would become endothermic and since energy is not created nor destroyed the amount of energy released on the exothermic side would be equal to the energy absorbed on the endothermic side
what is the equation for energy released
the energy released = mass of water heated x specific latent heat x rise in temperature
how can you compare the energy released in fuels
not all fuels release the same exact energy when they are burned some release more and some release less, but it Is very important to find the energy release in fuel to find out which fuel is more suitable to use on a particular machine.
Sample method:
Set up the copper can and tripod
Measure out 50cm3 of water into the can. Record the temperature.
Record the mass of a spirit burner of paraffin or hexane (including lid).
Place the spirit burner under the can on a heat-proof mat and light the wick. Heat for 2 minutes.
Record the temperature rise of the water and the mass of the spirit burner after (and lid).
Repeat for the second fuel (change the water).
higher rise and more mass loss = more energy release
