enthalpy

What is an exothermic reaction

a reaction that gives out thermal energy to the surroundings

how to identify an exo reaction

a rise in temp in surroundings

what happens to temp of system in an exo reaction

decrease in temp

what is an endothermic reaction

reaction that takes in thermal energy from the surroundings

how to identify an endo reaction

fall in temp of surroundings

what happens to temp of system in endo reaction

temp rise

what is the law of conservation of energy

energy cannot be created or destroyed only transferred

give 2 examples of types of endothermic reactions

dissolving, neutralisation

give 2 examples of types of exothermic reactions

combustion , displacement

what do energy level diagrams show

the relative energy and changes in energy of reactants and products in a reaction

what type of reaction is shown

exothermic

what is activation energy

minimum amount of energy the reactants need to collide with each other and react

what type of reaction is shown

endothermic

where do we draw the line from and to for ΔH on the E.L. diagram

from the reactants to the products

where do we draw the line from and to for Ea on the E.L. diagram

from the reactants to the top of the curve (to direction of products)

is the ΔH +ve or -ve for each reaction and why

\+ve for endo and -ve for exo bc represents the enrgy either being released (exo) or taken in (endo)

do products have more or less energy than reactants for both

less for exo and more for endo

what is the symbol Q + units

heat energy change , J

what is the symbol m +units

mass of substance being heated, g

what is the symbol + units for ΔH

enthalpy change (heat transfer/mole) , KJ/mol

what is the symbol + units for c

heat capacity → 4.18 , J/g/°C

what is the symbol + units for ΔT

temp change, °C

what is the equation linking heat change , heat capacity, mass and temp change

Q= mc ΔT

what is the equation linking mass, moles and mr

moles=mass/mr

what equation links enthalpy change, moles and heat change

ΔH= -Q/moles

what is the density of water

1g/cm3

how do you measure energy transferred in a reaction for displacement, dissolving and neutralisation

take start temp of 2 reactants , mix in polystyrene cup inside a beaker w a lid (cotton wool optional) , stirring , record most extreme end temp (max or min)

how do you measure energy transferred in a reaction for combustion

weigh mass of spirit burner and lid and vol of water , then burn the fuel in spirit burner placed under a copper can filled w water, getting heated by the flame. weigh spirit burner and lid again and vol of water. calculate delta H

how to improve diss,disp,neut experiment

cotton wool in beaker for insulation of heat ,lid reduces heat loss by evaporation , be consistent stirring

how to improve combustion experiment

use a screen to reduce draughts, dont do next to a window , so amap heat goes to heating water,, make sure to be consistent with whether you weigh the lid or not