Energetics Flashcards
1
Q
- Define enthalpy change
A
- Enthalpy change is the amount of heat energy taken in or given out during any change in a system provided the pressure is constant
2
Q
- What is an exothermic change?
A
- Energy is transferred from the system (chemicals) to the surroundings
3
Q
- What is an endothermic change?
A
- energy is transferred from the surroundings to the system (chemicals).
4
Q
- Define the standard enthalpy change of formation
A
- enthalpy change when 1 mole of the compound is formed from its elements under standard conditions (298K and 100kpa), all reactants and products being in their standard states
5
Q
- Define the standard enthalpy change of combustion
A
- enthalpy change that occurs when one mole of a substance is combusted completely in oxygen under standard conditions. (298K and 100kPa), all reactants and products being in their standard states.
6
Q
- State 4 factors which constitute standard conditions
A
- 100 kPa pressure; 298 K; Solutions at 1mol dm-3 ; all substances should have their normal state at 298
7
Q
- What does incomplete combustion produce?
A
- Soot (carbon), carbon monoxide and water.
8
Q
- What is ∆H for exothermic reactions?
A
- Negative
9
Q
- What is ∆H for endothermic reactions?
A
- Positive
10
Q
- What’s the equation for working out enthalpy change experimentally?
A
- energy change = mass of solution x heat capacity x temperature change
11
Q
- What’s the unit of specific heat capacity?
A
- J g-1K-1
12
Q
- What’s the units of temperature change?
A
- K
13
Q
- With calorimetry, why is a polystyrene cup placed into a beaker?
A
- Insulation and support
14
Q
- What do we do in calorimetry if it is difficult to obtain the final temperature?
A
- Take readings at regular time intervals and extrapolate the temperature curve/line back to the time the reactants were added together
15
Q
- What are 4 errors in using the polystyrene cup method of calorimetry to measure the enthalpy change?
A
- Heat transfer from surroundings (usually loss); The method assumes all solutions have the heat capacity of water; neglecting the specific heat capacity of the calorimeter- we ignore any heat absorbed by the apparatus; reaction or dissolving may be incomplete or slow; Density of solution is taken to be the same as water