DF1 Flashcards
What is an exothermic reaction?
A reaction that gives out energy and heats the surroundings.
What is an endothermic reaction?
A reaction that takes in energy and cools the surroundings.
What is enthalpy change?
The energy transferred to and from the surroundings.
How do you work out the enthalpy change of a reaction?
delta H = H(products) - H(reactants)
Is enthalpy change positive or negative for an exothermic reaction?
Negative - energy lost to surroundings.
Is enthalpy change positive or negative for an endothermic reaction?
Positive - energy gained from the surroundings.
What is a system?
Reactants and products of a reaction that you are interested in.
What is enthalpy change affected by?
- temperature
- pressure
- the concentration of solutions
What are standard conditions?
The set conditions to allow us to compare enthalpy changes.
What are the standard conditions?
- temperature (289K or 25℃)
- pressure (100kPa)
- concentration (1 mol dm-3)
- standard states
What is standard state?
The physical state of a substance under standard conditions.
How do you convert from degrees celsius (℃) to kelvin (K)?
Add 273 onto celsius reading.
What is the standard enthalpy change of a reaction?
The enthalpy change when molar quantities of reactants, react together under standard conditions.
How can enthalpy change be measured in labs?
- Transfer the energy (involved in the reaction) to or from the water surrounding the reaction vessel.
- Exo: water gets hotter
- Endo: eater gets cooler
- Measure temp and mass of water then calculate energy transferred (using equation).
How is a bomb calorimeter used to measure energy changes?
- Fuel is ignited electrically - burning in oxygen inside pressurised vessel.
- Energy transferred to surrounding water, and temperature change measured.
- Carried out at constant volume in closed container.
What is the standard enthalpy change of combustion?
The enthalpy change that occurs when one mole of a substance is burnt completely in oxygen (under standard conditions in standard states).
Is the standard enthalpy change of combustion positive or negative?
Exothermic so always negative.
What is the standard enthalpy change of formation?
The enthalpy change when one mole of a compound is formed from its elements (under standard conditions in standard states).
Is the standard enthalpy change of formation positive or negative?
May be positive or negative.
What is the standard enthalpy change of neutralisation?
The enthalpy change when one mole of H+ reacts with one mole of OH- to form one mole of water (under standard conditions and in solutions containing 1 mol/dm3).
How is the standard enthalpy change of neutralisation measured?
Can be measured from the energy given out when acids react with alkalis in aqueous solutions.
