Topic 8-Thermodynamics/Energetics I

Energy is being released to the surroundings and this means bonds are being formed An example of exo is combustion

Endothermic reactions are when energy is taken in and this means bonds are being broken Photosynthesis is an example

Energy can neither be created or destroyed but transferred from one to another

Minimum amount of energy required for a reaction to occur

Total EOR=Total EOP + energy lost or gained

Measure of heat content of a substance at a constant temperature and pressure KJ/mol

Enthalpy is directly proportinal to stochiometry If all moles of substance are doubled than Enthalpy is doubled

Enthalpy Change when One mole of a substance is formed in its standard state from its elements in their standard states

When one mole of a substance undergoes complete combustion under standard conditions Where all reactants and products are in their standard states

Involves the practical determination of enthalpy changes usually involves heating or cooling known amounts of water Used to work out enthalpy change of combustion

Energy=mass×SHC×change in temp

Heat lost to surroundings-not all heat is transferred to fuel Incomplete combustion-fuel may not burn properly Evaporation of fuel-some fuels evaporates instead of combusting Heat absorbed by calorimeter

Temp is taken every 30s for 3 min to ensure the change in temp is constant Reactants are mixed after 3 mins Let reaction complete Further readings taken every 30s as reaction cools,so change in temp is decreasing We extrapolate to calculate value of change in temp

We extrapolate as energy is being lost due to ongoing reaction,so by extrapolating the graph so its perpendicular to constant temp,we mitigate this and make it more accurate

Enthalpy change when an acid and alkali react together under standard conditions to form 1 mol of water

Enthalpy change when a reaction occurs in molar quantities shown chemical equations

It’s harder to measure the temperature change of a reaction when one the reactants is a gas A calorimeter helps with finding the temperature change Use equation q=mct

The total enthalpy change is independent of the route taken The total enthalpy change is always the same no matter of the route taken

Pipette 25cm³ of acid into a polysterene cup and measure the temperature Add 1 mol/dm³ of NAOH from a burette in 2cm³ portions,starring and measuring the temperature each time Ads 8cm³ of acid after max temp has been reached Plot a graph of volume of acid with temperature Extrapolate the graph and find the intersection

Amount of energy required to break 1 mol of a bond type in a molecule in gaseous state

Amount of heat energy taken in or given out during any change in a system provided the pressure is constant

Weight the fuel before and after burning Fuel is burned to raise the temp of water by a specific amount Some energy is lost and energy from fuel is transferred Place a lid to prevent heat loss

Place one of the reactants into a polysterene cup and place a thermometer Start a stopwatch and record temp of liquid every minute After 4 mins Add second reactant Continue taking temperature readings every minute for 10 minutes Plot a graph and extrapolate to find Enthalpy change.

Enthalpy of reactants- enthalpy of products