Calculating heat energy

Question 1

specific heat energy

Answer 1

a measure of a substance of the amount of energy (J) needed to increase the temperature of a specific quantity of that substance (usually 1g) by 1°C

Question 2

equation (chemical) to calculate heat energy (J)

Answer 2

q=mxcxΔ T

Question 3

worded equation to calculate heat energy

Answer 3

amount of heat energy (J) = mass (g) x specific heat capcity (Jg-1°C-1) x change in temperature (°C)

Question 4

what is the experimental determination of heat of combustion

Answer 4

a typical sample calorimeter is used to measure temperature changes in water. A fuel is burnt and the heat released by the combustion reaction increases teh heat content of the water

Question 5

steps in the use of a calorimeter

Answer 5

1. Measure the volume and initial temperature of water
2. measure the mass of the spirit burner and fuel
   3.light and burner and heat the water, stirring continuously
3. after some time, extinguish the burner and record the highest temperature brecahed by the water
4. measure the mass of the burner and remaining fuel, deduce the mass of fuel consumed

Question 6

equation (chemical) to calculate heat of combustion

Answer 6

ΔHc = q/n

Question 7

worded equation to caculate heat of combustion

Answer 7

heat of combustion (KJ mol-1) = heat energy released by sample or energy transferred to water (KJ) / amount of fuel burnt (mols)

Question 8

why are teh calculated heat of combustion values less than in actuality

Answer 8

because subtantial heat loss occurs when the experiment occurs

Question 9

steps in calculating heat of combustion from calorimeter

Answer 9

1. record the mass and change of temperature of the water
2. calculate the energy released using the formula q=mcΔT
3. calculate the number of moles of the substance conbusted using n=M/m
4. calculate the heat of combustion using ΔHc=q/n

Question 10

how does heat loss occur in calorimetery

Answer 10

some heat is lost to the surroundings, some heat is absorbed by the calorimeter

Question 11

ways to minimise heat loss in calorimetery

Answer 11

calorimeter should not be placed too far above the flame, a lid is placed over the calorimeter, insulating the beaker of water, placing insulation around the burning fuel (although sufficient oxygen to reach the fuel)

Question 12

what are the main sources of error in calorimetery

Answer 12

heat losses and incomplete combustion