energetics
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in an endothermic reaction,
energy is taken in from the surroundings
in an exothermic reaction,
energy is released into the surroundings
in an exothermic reaction, temperature of the surroundings
increases
what are 2 examples of exothermic reactions
combustion and neutralisation
in endothermic reactions, temperature of the surroundings
decreases
what is an example of an endothermic reaction
thermal decomposition
how do you remember if energy goes in or out in exo and endo reactions
EXO = EXits ENDO- in
what is the law of conservation of energy
energy cannot be created or destroyed but it can be transferred
displacement reactions are endo or exo
can be both
neutralisation reactions are endo or exo
always exothermic
combustion reactions are endo or exo
always exothermic
what are the 2 types of calorimetry experiments
enthalpy changes of reactions in solution enthalpy changes for combustion
to calculate the amount of energy produced by a chemical reaction in solutions what do we do
• measure the temperature change when the solutions are mixed together • the solutions need to be mixed together in an insulated container to prevent heat loss
the method for reactions in solutions can be used for (3)
• neutralisation reactions • dissolving solids • displacement reactions
what is the specific heat capacity of water
4.2
what is the density of water
1 g/cm³
in calorimetry experiments, what do we take for granted / assumptions (4)
• the specific heat capacity of the solution is the same as pure water (4.2) • density of solution is same as pure water (1 g/cm³) • reaction is complete • specific heat capacity of the container is ignored
A calorimeter can be made up of and why
a polystyrene drinking cup, a vacuum flask or a metal can because they’re insulating materials
how do you carry out a simple calorimetry experiment
• have a polystyrene cup with a plastic lid to prevent heat loss • add one reagent • have a thermometer there and measure initial temperature • add the second reagent and stir continuosly • record the maximum temperature it reaches and record the rise • record energy released using Q=mcΔT
equation for energy released
Q = m x c x ΔT
what does Q stand for and units of measurement
heat energy change, J
what does m stand for and units of measurement
mass of the substance being heated, g
what does c stand for and units of measurement
specific heat capacity, J/g/°C
what does ΔT stand for and units of measurement
temperature change, °C