9 Enthalpy Changes Flashcards
What does ΔrH stand for?
enthalpy change of reaction
What is the enthalpy change of formation (ΔfH)?
the enthalpy change when one mole of a substance is formed from elements
Is a reaction exothermic or endothermic if ΔH is negative?
exothermic
If energy is released during a reaction is it endothermic or exothermic?
exothermic
When can Hess’ law be applied?
when the enthalpy change can not be measured directly
What is the equation for determining the energy release that can be measured by a calorimeter?
q = mcΔT
Is a reaction exothermic or endothermic if ΔH is positive?
Endothermic
How can the estimated temperature change immediately after mixing two liquids be found?
extrapolate a graph backwards
What is activation energy?
the minimum value of energy needed to break the required bonds and start the reaction
How can inaccuracies in a calorimeter be reduced?
reduce energy loss/ensure complete combustion
What is the enthalpy change of combustion (ΔcH)?
the enthalpy change when one mole of a substance is burnt completely in oxygen
What are standard conditions in a reaction?
100 kPa and a stated temperature
What is the symbol for enthalpy change of neutralisation?
ΔneutH
What units is enthalpy measured in?
kJ mol−1
What is Hess’ law?
the start and end of a reaction are important but not the route taken to get there
Is a reaction endothermic or exothermic if energy is taken in during the reaction?
endothermic
What is needed to break bonds in molecules?
energy needs to be taken in
What is specific heat capacity?
the amount of energy needed to increase the temperature of 1 g of a substance by 1 K
How is the enthalpy change in a reaction calculated?
calorimetry/Hess’ law/difference between energy released by bond formation and energy taken in by breaking bonds
What is the standard enthalpy of formation (ΔfH⦵)?
the enthalpy change when one mole of a substance is formed from elements (in their standard states) under standard conditions
