energetics Flashcards
what is the definition of enthalpy change
heat/energy change under constant pressure
what are the standard conditions
temp - 298 k (25 degrees celcius)
pressure - 100kPA (100,00 pa)
what is an exothermic reaction
heat out
what is an endothermic reaction
heat taken in
what requires more energy, breaking or making bonds
breaking bonds more energy so endothermic
in calorimetry, why is the reading in the data book and the actual reading different
due to heat transfer and incomplete combustion
what is the calorimetry equation
q = mc∆T
what is the definition for hess’ law
the enthalpy chante for a reaction is independant of the route taken
what is enthalpy of formation
when 1 mole of a compound is formed from its constituent elements in their standard states and under standard conditions
what is enthalpy of combusiton
when 1 mole of a compound is burned completely in oxygen with all reactants and products in standard states and under standard conditions
suggest one possible risk to a person who uses a hand-warmer containing sodium hydroxide and hydrochloric acid.
container can spilling and releasing irritant, they are both very corrosive
one version of an iron-oxygen hand warmer advertises that it is designed to stay warm for up to four hours. Other than by increasing the amount of iron in the container, state one change to the iron in the hand-warmer that would increase this time. Explain why this change to the iron might not be an advantage. (ps. from a previous part, the iron was in a powdered form)
change in iron : decreasing the iron’s surface area
explanation : it might not be the best because the reaction will happen slower
state the meaning of the term molecular ion
a molecule with an electron that is knocked off
state one condition necessary for enthalpies of formation to be quoted as standard values at a specified temperature of 298K
- the pressure must be at 100kPa
- the reactants and products must be in their standard states
state why the standard enthalpy of formation of oxygen is zero
formation is for compounds, oxygen is an element so it doesnt need energy to form itself again
bond dissociation equation
sum of bonds broken - sum of bonds made
mean bond enthalpy equation
the enthalpy change needed to break the covalent bond into gaseous atoms, averaged over different molecules
