r1.1 measuring enthalpy change Flashcards
what is the difference between the system and the surroundings?
the system is typically all the reactants and products of a chemical reaction.
the surroundings are everything else around that is not the system.
universe = system + surroundings
what is heat?
heat, q, is a form of energy. it is the total energy of all the particles in an object.
measured in joules or kilojoules
how does heat transfer?
heat always transfers from a higher temperature object to a lower temperature until a thermal equilibrium is met
what is temperature?
temperature, T, is how hot or cold an object is. it is the average kinetic energy of the particles in an object.
measured in kelvin, celcius or farenheit
how does heat change with volume?
as heat is a measure of the total energy of the substance, heat will depend upon the amount of substance present. two different beakers might have the same average kinetic energy (temperature), but the larger volume of water has more heat
what is the difference between endothermic and exothermic reactions?
chemical reactions that involve the transfer of heat between the system and the surroundings and described as endothermic or exothermic.
chemical reaction that release heat to the surroundings are called exothermic (bond making, combustion, neutralisation).
chemical reactions that take in heat from the surroundings are endothermic (bond breaking, photosynthesis, melting)
what is the standard enthalpy change for a reaction?
standard enthalpy change for a reaction (ΔHө) is the enthalpy change that occurs when a chemical reaction is carried out at a constant pressure under standard conditions with all reactants and product in their standard states
what is the standard enthalpy change of combustion?
standard enthalpy change of combustion (ΔH꜀ө) is the enthalpy change when one mole of a substance burns completely in oxygen
what is the standard enthalpy change of formation?
standard enthalpy change of formation (ΔHfө) is the enthalpy change upon the formation of one mole of a substance from its constituent elements in their standard state.
what happens in an exothermic reaction?
in an exothermic reaction, energy flows from the system to the surroundings (released). the temperature of the surroundings increases. the enthalpy of the products is smaller than the enthalpy of the reactants, so the products are more energetically stable. the enthalpy change is negative.
what happens in an endothermic reaction?
in an endothermic reaction, energy flows from the surroundings to the system (absorbed). the temperature of the surroundings decreases. the enthalpy of the reactants is smaller than the enthalpy of the products, so the reactants are more energetically stable. the enthalpy change is positive.
how can you measure enthalpy changes?
enthalpy of reaction can be measured experimentally using a calorimeter. an expanded polystyrene cup can be used as a calorimeter as polystyrene foam is a good insulator and will prevent heat from the reaction being lost.
how do you calculate heat energy?
q = mcΔT
the heat energy absorbed or released in a chemical reaction will cause the temperature of a known mass of water to be lowered or raised.
how do you calculate enthalpy change?
ΔH = q / n
what is the standard enthalpy change of dissolution?
standard enthalpy change of dissolution (ΔHₛₒₗө) is the enthalpy change when 1 mole of an ionic substance dissolves in water to give a solution.
what is the standard enthalpy change of neutralisation?
standard enthalpy change of neutralisation (ΔHₙө) is the enthalpy change when a strong acid and strong base are reacted together to form one mole of water under standard conditions.
