Energetics Flashcards
(15 cards)
What is the energy conversion in an exothermic reaction
Chemical to heat
Do the products have less or more energy than the reactants in an exothermic reaction
Less - the remaining is lost to the surroundings
What is delta H called?
The molar enthalpy change
Is delta H negative or positive in an exothermic reaction
Negative
How to determine specific heat capacity (chemistry)
Q = mc delta T
Use 1g for mass
Specific heat capacity of water = 4.18 or 4.2
What are some potential issues with an experiment involving specific heat capacity
- Some heat will be lost to surroundings
- Incomplete combustion
- Water evaporation + energy required to heat vessel water is in
What is the setup for a SHC question
Spirit burner with an alcohol in is held under a copper can with water in and with a thermometer in.
How to measure the enthralpy change in solution
- Measure temperature of reagents
- Mix them together in an insulated polystyerine cup
- Record the temperature change
- The SHC of the final solution is assumed to be that of water (4.18)
Is breaking bonds exothermic or endothermic and why
It requires energy so it’s endo
Is making bonds exothermic or endothermic and why
It releases energy so is exothermic
How to work out enthralpy change based on bond energies
Bonds broken - bonds made
What must you not forget when calculating bond energies
Make sure to account for how many of that bond is present e.g. CH4 has 4 C-H bonds
What is on the x and y axis for an energy level diagram
Y = energy
X = extent of reaction
How to calculate total energy change based on bond energies
Total energy change = Bonds broken - bonds made
What must you always remember when doing SHC questions
M is the mass of the thing that is being heated, not the mass of the fuel burnt
