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.
