5.1 Measuring Energy Changes Flashcards
What is heat?
A form of energy.
What is temperature?
A measure of the average kinetic energy of particles.
What is an exothermic reaction?
Heat energy is transferred from a system to the surroundings so the surroundings get hotter the enthalpy change is negative.
What is an endothermic reaction?
A system takes what energy in from the surroundings so the surroundings get cooler the enthalpy change is positive.
What are the standard conditions?
100kPa and a specified temperature.
What is the standard state?
The pure substance at 100kPa and a specified temperature.
What is important about the energy in a chemical reaction?
It is conserved.
How can we measure the enthalpy changes of a reaction experimentally?
By measuring the temperature change of a substance and using the equation Q=mcdeltaT
What is the standard enthalpy change of combustion?
The enthalpy change when one mole of a substance is completely burnt in oxygen under standard conditions.
Why are there difference in the literature and experimental value of enthalpy changes?
Heat loss to the surroundings including heat needed to heat up the calorimeter
Incomplete combustion of the alcohol
Evaporation of the alcohol
Evaporation of water
What is the enthalpy change of solution?
The amount of heat energy given out/taken in when 1 mole of solute dissolves in excess solvent.
How can enthalpy changes involving solution be measured experimentally?
Measure out known amounts of reagents, record their initial temperatures, mix together the reagent in a polystyrene cup and record the maximum/minimum temperatures.
