How do you calculate the energy in food from a burning experiment?
Reveal answer
Energy (J) = mass of water (g) × 4.2 × temperature rise (°C); divide by mass of food (g) for J/g.
Key words: 4.2 · temperature rise
2(e) NUTRITION · RECALL
2.33B Energy content of a food sample
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Why is the measured energy lower than the label value?
Reveal answer
Heat is lost to the air and the tube, and the food may not burn completely.
Key words: heat lost
What is meant by the term calorimetry?
Reveal answer
Estimation of energy transfer by measuring a temperature change.
Key words: calorimetry
What is meant by the term specific heat capacity?
Reveal answer
Energy needed to raise 1 g of a substance by 1 °C.
Key words: specific heat capacity
What is meant by the term temperature change?
Reveal answer
Final temperature minus initial temperature.
Key words: temperature change
What is meant by the term systematic error?
Reveal answer
A consistent bias shifting measurements in one direction.
Key words: systematic error
What is meant by the term energy per gram?
Reveal answer
Energy estimate divided by the mass of sample burned.
Key words: energy per gram
Variables and quality checks: for Independent variable, give the operational choice and the reason.
Reveal answer
Operational choice: Food type. Reason: Compare different energy stores.
Key words: Independent variable
Variables and quality checks: for Dependent variable, give the operational choice and the reason.
Reveal answer
Operational choice: Calculated J g⁻¹ or kJ g⁻¹. Reason: Corrects for different masses burned.
Key words: Dependent variable
Variables and quality checks: for Control variables, give the operational choice and the reason.
Reveal answer
Operational choice: Water mass, gap, container and stirring. Reason: Keep heat capture comparable.
Key words: Control variables
Variables and quality checks: for Repeats, give the operational choice and the reason.
Reveal answer
Operational choice: At least three usable trials per food. Reason: Estimate variability and a mean.
Key words: Repeats
Variables and quality checks: for Safety, give the operational choice and the reason.
Reveal answer
Operational choice: Goggles, forceps, heatproof mat, tied hair. Reason: Reduce burn, fire and eye risk.
Key words: Safety
True or false, and why? “The largest temperature rise proves the food has the most energy per gram.”
Reveal answer
False. Account for water mass and mass of food burned.
True or false, and why? “Repeats eliminate heat loss.”
Reveal answer
False. Repeats reduce random uncertainty; systematic losses remain.
True or false, and why? “The water receives all energy released.”
Reveal answer
False. Much energy heats the apparatus and surroundings.
True or false, and why? “Food that will not relight has fully combusted.”
Reveal answer
False. Residue and incomplete combustion may remain.