unit 3: energy changes and rates of reaction

please we got this

accuracy

how close a measurement is to the accepted value

% error

[(accepted value - experimental value) / accepted value] x 100

the lower the %error, the more accurate the measurement

precision

the variation in results obtained when an experiment is repeatedly performed with the same equipment and procedure

(the smaller the variation, the more precise the results)

sig figs

give some indication of the precision of a measurement

uncertainty values

more exact indication of precison.

In addition to the sig figs, indicates how uncertain the last digit in the measurement is.

%uncertainty

an uncertainty value can be expressed as a percentage of the measurement

adding/subtracting uncertainty values

always add the uncertainty values

kinetic energy of a substance

any molecular movement (vibrational, rotational, translational)

potential energy of a substance

energy in bonds (ex hydrogen, covalent)

enthalpy (ΔH)

the amount of energy gained or lost in a substance

types of enthalpy changes

1. physical change

2. chemical change

3. nuclear change

physical change

breaking or forming bonds between molecules (ex: dispersion forces)

ex: H2O(l) —> H2O(g)

ΔH =. 10 - 1000kJ

chemical change

breaks and forms bonds inside molecules (ex: covalent bonds)

eg: H₂(g) + O2(g) → 2H2o(g)

ΔH =. 10^4-10^6 kJ

nuclear change

breaks and forms bonds inside atoms

ex: any nuclear formula thinngy

ΔH =. 10^9-10^10kJ

these changes can be:

exothermic or endothermic

exothermic changes

ΔH = -

Heat is released

energy of products is less than energy of reactants

endothermic changes

ΔH = +

Heat is absorbed

energy of products is higher than energy of reactants