How do you convert from grams to calories?

Question

How do you convert from grams to calories?
I'm burning biodiesel oils, and i got the amount of oil that was burned, but how do I convert from grams to calories?

Well this is basically my steps:

3. Pour 15ml of the fuel into an alcohol burner.
4. Mass the alcohol burner, wick, and fuel on a triple beam balance.
5. Pour 50ml of distilled water into a tin can.
6. Allow the wick to absorb the fuel.
7. Measure the temperature of the distilled water.
8. Ignite the wick and place alcohol burner immediately under the tin can.
9. Burn the fuel until the distilled water rises 5 degrees from its original temp.
10. Extinguish the flame immediately to keep the mass the same.
11. Mass the alcohol burner, wick, and remaining biodiesel.
12. Subtract the results from the mass of the alcohol burner, wick, and original amt. of fuel.
13. Mass a 10ml graduated cylinder.
14. Add the mass of the burned fuel to the mass on the triple beam balance.
15. Pour fuel to the graduated cylinder until calibrated.
16. Measure the amount of fuel in ml that is equal to the mass of the burned fuel.
17. The volume of fuel needed to heat the sample determines the caloric value.

I receive the caloric value in grams. Sorry if I'm repeating the question, but how do I convert that value to calories?

Answer 1

Presumably, you want to know how much energy is produced by burning a gram (or other unit of measure) of fuel. This is usually called the "energy content" or "heating value" of the fuel, and it comes in two "flavors": the "higher heating value", which is the that's released if one cools the combustion products back to room temperature (this value comrresponds to the heat or enthalpy of combustion one uses in chemistry); and the "lower heating value", which is the energy released if one let the combustion products escape at high temperature, e.g., as hot exhaust (thus carrying off some of the energy that might have otherwise been used). If you are combusting in a heater or engine, you probably want to use the "lower heating value".

The first answerer gave you the number of "dietary" or "food" calories in a gram of dietary fat. These "calories" are actually 1000 thermochemical calories (i.e., 1 food calorie = 1 kilocalorie).

The sources given below list various energy contents for biodiesel. Doing the appropriate energy, mass, and volume/density conversions gives a range of 9-10 kcal/gram, which is similar to the energy content of the input oils.

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Added in response to questioner's new comments.

You are trying to do "calorimetry", but you setup is far from ideal because much of the energy released by burning of the fuel doesn't go into heating the water. That is, there are too many ways for heat energy to escape the system without increasing the temperature of the water.

It takes 1 calorie to raise the temperature of 1 gram (= 1 ml) of liquid water at ~25 C by 1 degree C (or 1 kelvin). This quantity is called specific heat capacity of water. *IF* all the energy released by combusting the fuel went into heating the water, one could calculate the energy released by burning the fuel using the following formula:

(# ml or gm of water) * (temperature change of water) * 1 cal/(gm* degC)/(grams fuel used) = energy content per gram of fuel

In this case, for 50 ml = 50 gm of water that increases in temperature by 5 degrees C, the calorific value (the same as the heating value, and in this case the lower heating value because you're letting the hot combustion products escape from the system) is:

(50 gm * 5 C * 1cal/(gm*C))/(mass of fuel used) = (250 cal)/(mass of fuel used)

This will give you the heating value in cal/gm. If you'd rather express the heating value in terms of the volume instead of the mass of fuel, simply divide by the volume of the fuel used instead of the mass of the fuel used.

You don't specify, but I assume you're using degrees C, not degrees F. If you are using the Farenheit scale, a change of 5 deg F = a change of 2.778 deg C).

In reality, your setup will always underestimate the heating value of your fuel because you are losing heat from the system. The actual heating value will be higher (perhaps substantially so) than what you measure.

Answer 2

You can't because they measure different things. Grams measures mass (how much there is of something). Calories measures energy (the ability to do work). There is no general correlation that I know of between energy and mass. For example, light things can have lots of energy or very little.

I think what you want to do is figure out the amount of energy released from burning your biodiesel oil, right? You have the grams of oil burnt. That oil released some heat which was (hopefully) absorbed by something, usually water encased in a calorimeter of some kind. Foam cups are often used as calorimeters in the classroom.

To get the calories:
1) Find out how much water (in grams) is in the calorimeter.
2) Find out the temperature of the water before the burning.
3) Find out the temperature of the water after the burning.
4) It takes 1 calorie to heat 1 g of water 1 degree Celsius. Thus, if there were 100 grams of water in the calorimeter and it was heated 15 degrees from the burning, then 1500 (15 * 100) calories would have been released.

Answer 3

Calories are a measure of heat energy
grams are a measure of mass

An equation that relates them:
Heat=mass x specific heat x change in temperature

You have to know or calculate the specific heat of the fuel that you are using

Answer 4

1 gram of fat = 9 calories

Answer 5

tricky stuff. research in the search engines. that could help!