Energy- Unit 5 Flashcards
How can you measure the energy change in a reaction?
Temperature change
Of a known mass of water
Examples of energy changes
Neutralization reactions
Combustion reactions
Displacement reactions
Calculate energy changes of a fuel per g
Energy change / mass of fuel used
What does each bit mean?
Energy Change = M x C x T
M= mass of water
C= 4.2 specific heat capacity
T= Change in temperature
What errors can be made?
Poor insulation
No lid
Read thermometer wrong
Calculated mass of water wrong
Exothermic reactions
Energy released to the surroundings
Increase temperature of surrounds
Energy given out
Endothermic reactions
Energy taken in from the surroundings
Decrease temperature of surrounds
Energy taken in
Activation energy
‘hump’ on energy level diagram
minimum energy for a reaction to take place
Catalyst effect
Lowers the activation energy
speeds up rate
more particles have enough energy to react
Positives of hydrogen as a fuel
Can be used for cars as fuels
Only produces water as a by product
Doesn’t effect global warming
Negatives of hydrogen as a fuel
Steam is need
Electrolysis is expensive
Can be explosive
Calculating bond energies
Bonds broken - bonds made
When are bond energies endothermic/exothermic
Positive energy is endothermic
Negative energy is exothermic
Bond energy- defintion
Energy needed to break one mole
of that covalent bond
Why is energy need at the start of a reaction?
To break the bonds
in reactants
