Question

if the quatity of heat requried to raise the temperature of 70g of a gas from 25 C to 35C at constant pressure is 725J the gas is ?

Answer 1

I'm misreading this question, what are you looking for? Lol

Answer 2

I am Looking the GAS Used

Answer 3

(a) H2 (B) N2 (C) O2 (D) Cl2

Answer 4

It means We have to Find the Molar Mass of the Gas used Here

Answer 5

@electrokid @.Sam. @Callisto

Answer 6

since pressure it constant, it's meaning that you don't need to worry about it.

Answer 7

Pressure and volume are inversely proportional.

Answer 8

Try and focus on the relationship of the info given. Does that make sense?

Answer 9

What formula do you know that can relate that...

Answer 10

Q=mc (T2-T1)

Answer 11

i can Only See This one..

Answer 12

@shubhamsrg

Answer 13

not the molar mass dude, u gotta find its specific heat. http://www.engineeringtoolbox.com/spesific-heat-capacity-gases-d_159.html and u may use this to find out your gas

Answer 14

Sorry for the late response, I was working on something last night. But yes, That's the formula you want to start.

Answer 15

@electrokid

Answer 16

@chmvijay

Answer 17

what value did you get for "c"?

Answer 18

Q = mc dT

725 = 70 *c * 10

C = 725/700

Answer 19

remember that since this is a gas at const. pressure you will get "C_p"

Answer 20

nice..
divide that with "R"

Answer 21

Why Divide by R ?

Answer 22

(make sure of the units)
you can either use a table to see which gas has that "C_p" value

or if you divide by "R" you will get a hint as to if it'd be a monoatomic or diatomic gas

Answer 23

C/R = 0.12

Answer 24

did you make sure you used the proper units?

Answer 25

the ratio should be >2

Answer 26

it is N2

Answer 27

:(

Answer 28

cp values for the given options: (J/gK)
a) 14.3
b) 1.04
c) 0.92
d) ?? (dont know)
source -> wiki

Answer 29

LOL:) with wiki we should not tell this y solving we should tell LOL

Answer 30

Using the values you quoted:

Q = mass * (temperature change)
725 = 70 * C * 10
C = 725/700 = 1.04 Joule per gram per Kelvin

cp values for the given options: (J/gK) a) 14.3 b) 1.04 c) 0.92 d)

so the measured heat capacity (at constant pressure) matches choice b most closely, making N2 the correct answer.

Answer 31

I am writing off the top of my bird-brain, so correct me if i am wrong.

Let's pretend these gases are ideal gases. so the "constant pressure" should not be much higher than 1 atm, the temperature should not be too low, yada yada.

For a diatomic gas, there are 6 degrees of freedom, so the heat capacity (*at constant volume*) or C_v should be

6*1/2 R Joules per mol per Kelvin.

why six degrees of freedom? roughly speaking, because there are 3 degrees of freedom for translation, 2 for rotation, 1 for vibration.

for an ideal gas, the molar heat capacity at constant *Pressure* is

heat capacity at constant *Volume* + R

so C_p = 4 R Joule per Kelvin per *mole*

Now the specific heat is in units of Joule per Kelvin per *gram*, so we need to convert the unit:

specific heat = C_p / (molecular weight)

and we see that the unit comes out to be correct. plugging in the values for the examples you gave, we can estimate the specific heats:

H2: 17 (versus the measured value of 14.3)
N2: 1.2 (1.04)
O2: 1.0 (0.92)
Cl2: 0.47

the unit is in Joules per Kelvin per gram. i put the measured value in bracket. The estimated values are a bit off, but they show why the specific heat decreases as the molar mass increases.