Measuring Enthalpy Changes Flashcards
What is standard molar enthalpy of formation
The enthalpy change when one mole of a compound is formed from its constituent elements under standard conditions with both reactants and products in standard states(state you expect to find it in standard conditions)
What is standard molar enthalpy of combustion
The enthalpy change when one mole of an element or compound reacts in excess oxygen under standard conditions with both reactants and products in standard states
What is the standard enthalpy change of reaction
The enthalpy change when the reaction occurs in the molar quantities shown in the chemical equation under standard conditions in their standard states
What is temperature and how is it measured
The average KE of the particles in a system(as particles move faster their average KE increases and the temperature goes up), measured using a thermometer
Is temperature dependent or independent to the number of particles
Independent
What is heat
A measure of the total energy of all the particles present in a given amount of substances
Is heat dependent or independent pf the number of particles
Dependent on the number of particles present
Equation for energy transferred and units
Energy transfer = mass(g) pf solution or water x SHC of water (4.18J/g degrees Celsius) x change in temperature (degrees Celsius)
What is specific heat capacity
The amount of energy needed to raise the temperature of 1g of a substance by 1 degrees celcius
Specific heat capacity of water and solutions
4.18J/g degrees celcius
What is simple calorimetry
Used to compare the amount of energy produced by different fuels and foods by measuring the heat energy given out or taken in to heat up or cool down a known mass of water
Three measures you need to calculate enthalpy change using simple calorimetry
- Mass of substance being heated up which is often water
- Temperature change
- Specific heat capacity of substance
Why are the values found in simple calorimetry experiments usually not accurate
Usually a lot lower than the actual values as not all energy is transferred into the water as some is lost into the atmosphere
What is the bomb calorimeter and why is it more accurate than simple
Heat energy is trapped inside a sealed and insulated container to reduce heat loss to the surroundings and water is stirred continuously to make sure the heat energy is distributed evenly throughout
Do you use the total mass/volume of the mixture when calculating enthalpy change
Yes use the total volume or mass of the mixture
