[ruboxxx]

Hello all,  this is my first time ever taking a chemistry class.  My teacher has us using the Mastering Chemistry software and I'm pretty sure he's not making it easy on us.  I was wondering if it would be possible to get some help with some of the problems that he assigned to us on the homework.  I've attempted to figure out these problems, but have not come up with any luck.  Since he only gives us so many attempts of answering a question right I would like to get them all right. Here's the ones I'm having problems with:

-----------------------------------------------------------------------------------------------
A patient receives 2500mL of an IV solution containing 2g of glucose per 100 mL.

1.  How much energy, in kilojoules, does the patient obtain from glucose, a carbohydrate?
Express your answer to two significant figures and include the appropriate units.

2.  How much energy, in kilocalories, does the patient obtain from glucose?
Express your answer to two significant figures and include the appropriate units.

-----------------------------------------------------------------------------------------------

Using the following data, determine the kilocalories for each food burned in a calorimeter.

1.  One cup of popcorn that changes the temperature of 1.20×103g water from 28.5∘C to 52.7∘C

2.  A sample of olive oil that increases the temperature of 417g water from 25.6∘C to 41.7∘C

-----------------------------------------------------------------------------------------------


When a 1.30-g sample of ethanol (alcohol) is burned in a calorimeter, the heat released increases the temperature of 870 g of water in the calorimeter from 18.5 ∘C to 28.9 ∘C.


1.  What is the energy value, in kJ/g, of ethanol?

2.  What is the energy value, in kcal/g, of ethanol?

-------------------------------------------------------------------------------------------------


The combustion of 1.0 g of gasoline releases 11 kcal of heat (density of gasoline = 0.74 g/mL).

1.  How many megajoules are released when 1.9gal of gasoline burns?
Express your answer using two significant figures.

2.  When a color television is on for 2.0 h, 320kJ are used. How long can a color television run on the energy from 1.9gal of gasoline?
Express your answer using two significant figures.

---------------------------------------------------------------------------------------------------


Thanks for any help, if possible if you could post work so I can get a better idea of how you came up with that calculation to help me would help as well.

[Dan]

You must show you have attempted the question, this is a Forum Rule.

[ruboxxx]

Ok it's late here I will post my calculations in the morning when I wake up. Thanks!

[ruboxxx]

Ok sorry about that, this is what I came up with for my answers.  I'll post my results in red.

A patient receives 2500mL of an IV solution containing 2g of glucose per 100 mL.

1.  How much energy, in kilojoules, does the patient obtain from glucose, a carbohydrate?
Express your answer to two significant figures and include the appropriate units.

2500 mL (2g/100mL) = 50g

50g (4kcal/1g) = 200kcal

200 kcal (4.184J/1kcal) = 836.8J

836.8J (0.001kJ/1J) = 0.8368kJ  rounded to 2 significant figures would be 0.84kJ correct?


2.  How much energy, in kilocalories, does the patient obtain from glucose?
Express your answer to two significant figures and include the appropriate units.

2500 mL (2g/100mL) = 50g

50g (4kcal/1g) = 200kcal rounded to 2 significant figures would be 2.0 x 10² correct?

----------------------------------------------------------------------------------------------------------

Using the following data, determine the kilocalories for each food burned in a calorimeter.

1.  One cup of popcorn that changes the temperature of 1.20×10³g water from 28.5∘C to 52.7∘C

1.20 x 10³g (4.184J / 1g x 1 degree C)(52.7 degrees - 28.5 degrees) = 121503.36J

121503.36J (1 kcal/ 4.184J) = 29040 kcal rounded to 3 significant figures would be 29.0 x 10³ kcal correct?

2.  A sample of olive oil that increases the temperature of 417g water from 25.6∘C to 41.7∘C

417g (4.184J / 1g x 1 degree C)(41.7 degrees - 25.6 degrees) = 28090.1208J

28090.1208J (1 kcal / 4.184J) = 6713.7 kcal rounded to 3 significant figures would be 6.71 x 10³ kcal correct?


I'm working on the last 4 problems at the moment I will post my results when I'm done.  Thanks for any *delete me*

[Dan]

Using the following data, determine the kilocalories for each food burned in a calorimeter.

1.  One cup of popcorn that changes the temperature of 1.20×10³g water from 28.5∘C to 52.7∘C

1.20 x 10³g (4.184J / 1g x 1 degree C)(52.7 degrees - 28.5 degrees) = 121503.36J

121503.36J (1 kcal/ 4.184J) = 29040 kcal rounded to 3 significant figures would be 29.0 x 10³ kcal correct?

2.  A sample of olive oil that increases the temperature of 417g water from 25.6∘C to 41.7∘C

417g (4.184J / 1g x 1 degree C)(41.7 degrees - 25.6 degrees) = 28090.1208J

28090.1208J (1 kcal / 4.184J) = 6713.7 kcal rounded to 3 significant figures would be 6.71 x 10³ kcal correct?


I'm working on the last 4 problems at the moment I will post my results when I'm done.  Thanks for any *delete me*

Check your J  kcal conversions!

Think about what a sensible number is. Recommended energy intake for adults is about 2000 kcal/day. Does it seem sensible that a cup of popcorn stores 29000 kcal? The energy available through digestion is of course lower than that released on combustion, but still a comparison worth considering I think.

[ruboxxx]

Thanks, the first one should actually be 29.0 kcal without the 10³.

And the second one should be 6.71 kcal.