Energetics Flashcards
What are standard conditions?
100kPa
298 K
What unit is used to measure enthalpy change?
kJ mol-1
What is enthalpy change?
The heat energy transferred in a reaction at constant pressure
For exothermic reactions, is the enthalpy change positive or negative?
Negative, energy of products is lower
Give 2 examples of exothermic reactions
Combustion and respiration
State 2 examples of endothermic reactions
Thermal decomposition, photosynthesis
Why is enthalpy change positive for endothermic reactions?
As reaction takes in energy from the surroundings so products have more energy
What is bond enthalpy?
The energy required to break a bond
What is mean bond enthalpy?
The average energy needed to break a certain type of bond
Why do we use a MEAN bond enthalpy?
As similar bonds can require different amounts of energy to break depending on location
Define standard enthalpy change of formation
The energy change when 1 mol of a compound is formed from its elements in standard states and conditions
What is the standard enthalpy of combustion?
The enthalpy change when 1 mole of a substance is completely burned in O2 (standard states and conditions)
!!!!!!
What is calorimetry?
Experimenting on temperature changes in a reaction
What does the q stand for in
q = mc^T?
Heat loss/gain (joules)
What unit is temperature measured through in q = mc^T?
Kelvins
How do you convert Celsius to kelvins?
+ 273
State 2 common problems in calorimetry experiments
- Energy is always lost to surroundings
- Incomplete combustion may give out less energy
What is Hess’s Law?
Total enthalpy change for a reaction is independent of the route taken
