Energy topic

Fuel sources

100

Our main source of energy is _________________ (carbohydrate)

Glucose

200

The following equation represents: 

6CO₂ (g) + 6H₂O (l) --> C₆H₁₂O₆ (aq) + 6O₂ (g) 

a) photosynthesis

b) cellular respiration 

Also, identify what the missing reagents are? 

photosynthesis 

UV light + chlorophyll 

300

Is cellular respiration an endothermic or exothermic reaction? 

it is exothermic! 

400

Tom is running the 400m spring but half way through the race, his muscles in his leg start to cramp and feel sore. This can be caused by lactic acid build up in his muscles. Explain why this is happening to Tom.

Lactic acid can build up in the muscles when anaerobic respiration takes place whereby there is a high demand for oxygen but an insufficient supply of oxygen. As a result, waste material cannot be processes quickly enough.

500

Write the balanced chemical equation for the fermentation of glucose.

C₆H₁₂O₆ (aq) ----> 2C₂H₆OH (aq) + 2CO₂ (g)

                    yeast

Food molecules

100

What are the energy values for:

carbohydrates

protein

fats

carbohydrates: 16 kJ/g

protein: 17 kJ/g

fat: 37 kJ/g

200

What is metabolism?

Metabolism refers to all the chemical processes involved in using the food organisms consume to maintain life. 

300

Name two food molecules that do not offer any nutritional/ energy value?

water, minerals, vitamins and fibre

(any two in this list)

400

Name the monomer for each of the following macromolecules:

- carbohydrates

- proteins

- fats

carbohydrates: glucose (monosaccharide)

proteins: amino acid

fats: triglyceride

500

The reaction whereby a carboxylic acid and an alcohol reacts to together to form an ester is called ______________. 

Draw: ethanol + propanoic acid ---> 

Esterification 

Spirit burner cal

100

What is the specific heat capacity of water (including appropriate units)?

4.18 J/g/^oC

200

A fuel or food’s heat of combustion can be estimated by

A. determining the change in mass of water when the fuel or food is mixed with the water.

B. determining the change in mass of water when the fuel or food is combusted below it.

C. determining the change in temperature of water when the fuel or food is mixed with the water.

D. determining the change in temperature of water when the fuel or food is combusted below it.

D. The change in temperature of water can be used to measure the amount of energy released from a combustion reaction, and hence the fuel or food’s heat of combustion.

300

A spirit burner containing methanol initially weighs 237.6 g. After this fuel is used to heat 250.0 g of water, the spirit burner and remaining methanol now weigh 232.2 g. The mass of fuel combusted is

A. 5.4 g

B. 12.4 g

C. 237.6 g

D. 250.0 g

A.m(fuel combusted) = minitial(fuel + burner) − mfinal(fuel + burner)

m(fuel combusted) = 237.6 g − 232.2 g

m(fuel combusted) = 5.4 g

400

In an experiment to determine a fuel’s heat of combustion, 200.0 g of water increases in temperature from 22.3 ℃, to 49.8 ℃. What is the amount of energy absorbed by the water?

A. 18.6 kJ

B. 23.0 kJ

C. 41.6 kJ

D. 18 600 kJ

B. ΔT = Tfinal − Tinitial

ΔT = 49.8 ℃ − 22.3 ℃ = 27.5 ℃ 

m (water) = 200.0 g

c(water) = 4.18 J g−1 ℃ −1 

q = mc ΔT 

q = 200.0 g × 4.18 J g⁻¹ ℃ ⁻¹ × 27.5 ℃ 

q = 22 990 J 

q = 22 990 ÷ 10³ kJ 

q = 23.0 kJ (3 sig. figs)

Solution cal

100

The most simple solution calorimeter is called a ___________.

coffee cup calorimeter 

200

A calorimeter can more accurately estimate the amount of heat energy released by 

A. retaining energy in its walls. 

B. reducing the amount of heat used to heat the surrounding air. 

C. making the amount of heat loss more consistent and hence more measurable. 

D. All of the above options correctly complete the statement. 

D. Calorimeters minimise both the heat loss to the surrounding air (in part by retaining heat in their walls), and the amount of variation in heat loss, making it more consistently measurable

300

Han heats a quantity of water in a calorimeter for 150 seconds with a current of 1.3 A and a voltage of 6.0 V, causing the water temperature to rise by 2.1 ℃. 

The calibration factor for their calorimeter (in J ℃⁻¹) is closest to 

A. 19 J ℃−1 

B. 550 J ℃−1 

C. 560 J ℃−1 

D. 1200 J ℃−1 

C. q = VIt = 6.0 V × 1.3 A × 150 s = 1170 J

ΔT = 2.1 ℃

CF = q /ΔT 

CF = 1170 J/2.1 ℃ 

CF = 557.1 J ℃⁻¹

CF = 5.6 × 10² J ℃⁻¹ (2 sig. figs)

400

A chemist electrically calibrates a calorimeter by turning the heater on for 200 seconds.  (show image)

Using the more accurate extrapolation method, the value of ΔT for this experiment is 

A. 4.0 ℃ 

B. 4.5 ℃ 

C. 5.5 ℃ 

D. 6.5 ℃ 

C. The heater was turned on at t = 200 seconds. The temperature began decreasing at t = 500 seconds. Extrapolation of the line fitting the points from t = 500 seconds meets the point t = 200 at a temperature of 25.5 ℃. Therefore,  ΔT = 25.5 ℃ − 20.0 ℃ = 5.5 ℃

500

Solution calorimetry could be used to estimate the enthalpy change of which of the following reactions?

A. CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(l)

B. AgNO₃(aq) + HCl(aq) → AgCl(s) + HNO₃(aq)

C. 2H₂O(l) → 2H₂(g) + O₂(g)

D. MgCO₃(s) + 2HNO₃(aq) → Mg(NO₃)₂(aq) + CO₂(g) + 2H₂O(l)

B. Option B is a precipitation reaction. Options A, C, and D all are reactions that produce gas and hence cannot be conducted in a solution calorimete