Energetics Flashcards
Exothermic reaction
When energy is given out (usually as heat energy) but it can be given out as light, sound or even electrical energy aswell
What are exothermic process
Condensing and freezing
Process of the exothermic reaction
When a gas condenses to a liquid or a liquid freezes to a solid, energy is given our as new bonds between the particles form
Reactants
What’s going in
Products
What’s going out
Endothermic reaction
A reaction is described as endothermic when energy is taken in from the surroundings. It is observed by a drop in temperature of the surroundings
Endothermic process
When a solid melts to a liquid or a liquid boils to a gas, energy is taken into break the bonds between the particles
Endothermic processes
Melting and boiling
Why do reactions give out or absorb energy?
To break a chemical bind energy must be put intro the bond- endothermic
When a new chemical bond forms energy is released- exothermic
Mexobendo
Making- exothermic
Breaking- endothermic
Delta H Of the reaction=
E bond breaking - E bond making
If E bond breaking is less than E bond making then
- DELTA H
Exothermic
If E bond breaking is bigger than E bond making then
+ Delta H
ENDOTHERMIC
What does the bond energy measure?
The average amount of energy (in KJ/mol) needed to break a particular bond in the gas phase
Bond energies can be used to….
Estimate the enthalpy of a reaction
Q=
McdeltaT
Q
Heat energy (joules, J)
m
Mass of water
Specific heat
4.18 Jg-1 or oC-1
Delta T
Temperature change
To convert J to KJ
Divide by 1000
Delta H
= Q/n
n
Number of moles
Delta H
Enthalpy change (KJ mol-1)
N=
Moles= mass/rfm
Make sure volume=
Dm3
Moles = mass/rfm or
Concentration x RFM
In the the exothermic reaction, why does it take in heat?
Because breaking bond takes in energy, and making bonds gives out energy former exceeds the later
Why is the match needed to start the reaction, but once it continues without further heating
Match supplies the activation energy the reaction supplies it after that
Comparing the heat energy produced by combustion of various alchohols
1) fill conical flask with 100cm3 of water.
2) weigh the spirit burner and lid containing the alchohol and record the mass and name of the alchohol
3) record the initial temperature of the water using the thermometer.
4) place the spirit burner under the vincula flask and light the wick.
5) allow the alchohol to heat the water so the temperature rises by about 40oc
6) replace the cap after blowing out the flame
7) rewrite the spirit burner and cap and work out the mass of alcahol used
Repeat for different alcahol use 100cm3 of new water each time
Neutralisation caloritimatry experiment
1) measure out copper sulphate solution into a well insulated container and then measure its temperature. Add zinc powder. Stir gently and continuously and note the highest temperature reached. Work out the temperature change.
Then repeat part 1 using Citrix acid and sodium hydrogencarbonste, record the temp change as before
Methanol
CH3OH
Ethanol
C2H6O
Propanol
C3H8O
Example of an exothermic reaction
The thermit reaction
Delta H
Temp change
Example of an exothermic reaction
The thermit reaction
Delta H
Temp change
