measuring changes in chemical reactions - U3 AOS 1 Flashcards
1
Q
mass to mass stoichiometry
A
- determine molar mass of known and unknown
- convert known substance mass to mole
- use stoichiometry rations to find mole of unknown
- n(unknown) = unknown/known x n(known)
2
Q
mass to volume stoichiometry
A
- molar volume of gases is 24.8
- measured in L mol-1
- n=v/Vm
- density = mass/volume
3
Q
volume to volume stoichiometry
A
- all gases occupy the same volume at equal pressures and temperature
- v(known) = unknown/known x v(known)
4
Q
enthalpy changes
A
- energy released in kj mol-1 = molar heat of combustion x n(fuel)
- energy released in kj g-1 = heat o combustion x m(fuel)
- ensure to work out energy mole when one mole of fuel is combusted
5
Q
combustion and greenhouse gases
A
- combustion of carbon based fuels produces carbon dioxide, a greenhouse has which can absorb infrared radiation
- carbon dioxide contributes to increased global warming an the greenhouse effect
- methane also contributes to the global warming effect
6
Q
reducing the effect of greenhouse gases
A
- capturing methane gas from agriculture does increase the net volume of CO2 in the atmosphere but it reduces the effect of methane which is worse
7
Q
specific heat capacity
A
- the energy needed in joules to increase the temperature of 1 gram of a substance by 1 degrees
- water has a high specific heat capacity due to hydrogen bonding between water molecules
- high specific heat capacity means the substance is good a storing heat.
- measured in joules per gram per degrees
8
Q
specific heat capacity formular
A
q (J) = m x c x ΔT
c = 4.18
9
Q
estimating heat released
A
- a vessel can be filled with water and the mass and initial temp recorded. Once the fuel is combusted, the specific heat capacity of water can be calculated.
- heat of combustion = q/m(fuel)
- molar heat of combustion (kj/mol) = q/n(fuel)
- chance from j to kj
10
Q
calorimetry
A
- the use of a calorimeter to estimate the enthalpy change of a reaction that occurs in solutions
11
Q
calorimeter
A
- an insulated vessel designed to minimise and account for heat loss
12
Q
calibration factor
A
- the energy needed to be released/absorbed in a given calorimeter to increase/decrease water by 1 degrees
13
Q
chemical calibration method
A
- conduct an exothermic reaction with a known enthalpy change and amount of fuel, them measure the ΔTof the water.
- use stoichiometry to calculate the heat loss.
- q = n(fuel) x heat of combustion
- calibration factor = q/ΔT
- J/degrees
14
Q
electrical calibration method
A
- a calorimeter can be connected to an electrical heating element which can release a known amount of energy and the ΔT of the water can be measured
- q(J) = v x l x t
- CF = q/ΔT
- CF = vlt/ΔT
15
Q
using a calibration factor
A
- conduct the unknown reaction in the same calorimeter
- measure the ΔT of the water
- calculate the energy using q(J) = CF x ΔT
- q can be used to calculate the enthalpy change of the reaction.