3.1.4 Energetics Flashcards
What is an exothermic reaction
The reactions that release energy to the environment e.g. combustion
What is endothermic reactions?
Reactions that absorb energy from the environment e.g. photosynthesis
What is reaction is making and breaking bonds?
Making bonds is exothermic
Breaking bonds is endothermic
What do endothermic and exothermic graphs consistent of?
Endothermic: reactants lower than products
Exothermic: reactants higher than products
What is the standard temperature and pressure?
100kPa
298K / 25degreescelcious
What is standard enthalpy of combustion?
The enthalpy change when one mole of a substance is burnt completely in oxygen under standard conditions and all substances in their standard state
What is standard enthalpy of formation?
The enthalpy change when one mole of a substance is formed from its elements under standard conditions and all substances in their standard state.
How is change in heat energy calculated?
Energy change (kJ)
—————————-
Mol of reactant (mol)
How is energy calculated?
Q = m x c x change in T
What is calorimetry and what does it consist of?
The process of measuring the heat change for a given chemical process
It includes; thermometer, stirrer, insulated stopper, insulated cup, reaction mixture
What are the risk assessments involved in the change in heat temperature experiment? Include solutions
- solution is corrrosive to eyes
Wear goggles - solution is irritant to skin
Wear a lab coat
If solution goes on your skin you should wash well with plenty of water
Explain the steps to the calorimetry.
- weigh excess 2g of zinc
- pipette 25 cm3 of the 0.5mol/dm3 copper sulphate in a polystyrene cup that is inside a beaker
- place a lid on the cup and put a thermometer through the hole, stir and record the temp every minute
- at 4 minutes add the zinc to the cup, continue to stir and record temp every minute until 10 minutes
What is neutralisation?
The enthalpy change when one mole of water is formed by reacting an acid and alkali under standard conditions
Bond enthalpy change
The enthalpy change needed to break the covalent bond into gaseous atoms, averaged over molecules
