Chapter 2 - Measuring changes in chemical reactions

Question 1

stoichiometry

Answer 1

calculating amounts of reactants and products using a balanced chemical equation

Question 2

combustion

Answer 2

the rapid reaction of a compound with oxygen to produce carbon dioxide and water
Fuel + O2 -> H2O + CO2

Question 3

precision

Answer 3

refers to how close multiple measurements of the same investigation are to each other; a measure of repeatability or reproducibility

Question 4

accuracy

Answer 4

refers to how close an experimental measurement is to a known value

Question 5

molar gas volume

Answer 5

the volume occupied by a mole of a substance at a given temperature and pressure; at SLC, 1 mole of gas occupies 24.8 L

Question 6

ideal gas equation

Answer 6

PV = nRT, where pressure (P) is measured in kilopascals (kPa), volume (V) is measured in litres and temperature (T) is measured in kelvin (K). R = molar gas constant (8.31)

Question 7

pressure

Answer 7

the force per unit area that one region of a gas, liquid or solid exerts on another

Question 8

molar gas constant

Answer 8

the constant of the universal gas equation; R = 8.31 J mol−1 K−1 when pressure is measured in kPa, volume is measured in L, temperature is measured in K and the quantity of the gas is measured in moles (n)

Question 9

kelvin

Answer 9

the SI base unit of thermodynamic temperature, equal in magnitude to the degree Celsius

0*C = 273 K

Question 10

fuel

Answer 10

a substance that burns in air or oxygen to release useful energy

Question 11

efficiency

Answer 11

(of energy conversion) the ratio between useful energy output and energy input
%efficiency = output (aka amount of energy in useful form) / input (aka amount of potential energy in chemical form)

Question 12

calorimetry

Answer 12

a method used to determine the changes in energy of a system by measuring heat exchanges with the surroundings

Question 13

serving size

Answer 13

the recommended amount of food on a nutrition label for one serving

Question 14

specific heat capacity

Answer 14

the energy needed to change the temperature of 1 g of a substance by 1 °C
Specific heat capacity of water = 4.18

Question 15

solution calorimetry

Answer 15

the process of using a calorimeter to measure heat changes in a solution; for example, heat of dissolution and neutralisation reactions

Question 16

calorimeter

Answer 16

an apparatus used to measure heat changes during a chemical reaction or change of state

Question 17

change in enthalpy

Answer 17

the amount of energy released or absorbed in a chemical reaction

Question 18

dissolution

Answer 18

the process of solutes dissolving in solvents to form a solution (common chemical change that occurs in solution calorimeters)

Question 19

calibrated

Answer 19

adjusting an instrument using standards of known measurements to ensure the instrument’s accuracy

Question 20

calibration factor

Answer 20

the amount of energy required to change the contents of a calorimeter by one degree, with units J °C^–1
CF = energy released during calibration/temperature rise = VIt/ΔTc
where CF is measured in J/*C & temp rise (ΔTc) = final temp (ΔTf) - initial temp (Ti)

Question 21

electrical calibration

Answer 21

calibration of a calorimeter by supplying a known quantity of electricity

Question 22

chemical calibration

Answer 22

calibration of a calorimeter using a combustion reaction with a known ΔH. A known (measured) amount, in moles, or mass of reactant(s) is placed inside the calorimeter and ΔT is measured. The dissolution of solids can be used. Heat of reaction, such as the exothermic heat of neutralisation between a strong acid and base, can also be used.

Question 23

How to find moles when given a mass:

Answer 23

n=m/M
where ‘n’ = mol, ‘m’ = mass, and ‘M’ = Molecular mass

Question 24

How to fine moles when given a volume:

Answer 24

n=V/Vm
where ‘n’ = moles, V = volume, and ‘Vm’ = molar volume (24.8 at SLC)

Question 25

Volume-volume calculations

Answer 25

similar to mole-mole calculations V(unkown)/V(known = coefficient of unknown/coefficient of known

Question 26

calculating density

Answer 26

Density = mass/volume 1cm^3 = 1mL 1g/cm = 1g/mL

Question 27

How to find energy:

Answer 27

q=mcΔT where: - q = energy (measured in joules (J) - m = mass of *water* (not the food) in grams (g) - c = specific heat capacity of water (4.18 J/g *C - ΔT = change in temperature (*C)

Question 28

How to find the amount of energy released to calorimeter

Answer 28

E = VIt where: - E = (energy released (joules)) - V = potential difference (volts) - I = current (amps) - t = time (s)

Question 29

Steps to using a calorimeter:

Answer 29

From PowerPoint: - Measure and record the mass of water - Record the initial temperature of the water - Weigh your fuel source and place into the spirit burner - Light the spirit burner - Record the change in temperature - Stop heating before all the fuel is used From textbook: - Calibrate the calorimeter (this step can also be done at the completion of the reaction). - Measure the masses or volumes of the chemicals that are required for the reaction, ensuring that the volume of water or solutions used is the same as the volume used for calibration. - Measure the temperature of the water or solutions. - Add the solid or solutions to the calorimeter. - Record the highest or lowest temperature reached. - Perform the calculations. - If ΔH is required, remember to use the appropriate sign.

Question 30

How to find the energy change:

Answer 30

In solution calorimetry, the energy change is calculated using the following equation: Energy change = CF x ΔTr The ΔH is the energy change per mole. To find the ΔH, divide the energy change by the number of mole, n. ΔH = energy change/n aka ΔH = q/n