Question

Using the equations and enthalpy values provided, which mathematical expression can be used to determine the unknown enthalpy change represented by x?

3 C + 3 O2 yields 3 CO2 deltaH = x

4 H2 + 2 O2 yields 4 H2O deltaH = - 1144 kJ

C3H8 + 5 O2 yields 3 CO2 + 4 H2O deltaH = -2222 kJ

C3H8 yields 3 C + 4 H2 deltaH = 104 kJ

104 = (-2222) - [x - (-1144)]

104 = (-2222) - [x + (-1144)]

104 = (-2222) + [(-1144) - x]

104 = (-2222) - [(-1144) - x]

@aaronq think you could help please?

Answer 1

I'll give a medal :)

Answer 2

@SolomonZelman Do you think you could possibly help me? I understand if you're busy but I just dont understand this question at all.

Answer 3

I am really bad at chemistry. I used to be very good at it, but I forgot it since 10th grade, and my maximum capability in science is answering some biology questions about Punnet squares.

Sorry -:(

Answer 4

@SolomonZelman It's all good. @aaronq do you know any?

Answer 5

yep, i'm workin on it hold up

Answer 6

ok thanks.

Answer 7

This concerns Hess's Law. You have to arrange equations (1) through (3) to (4) to match the top equation (so that everything but what is there cancels out.

(1) \( 3 C + 3 O_2 \rightarrow 3 CO_2 ~~~~\Delta H_1 = x\)

(2) \(4 H_2 + 2 O_2 \rightarrow 4 H_2O~~~~ \Delta H_2= - 1144 kJ\)

(3) \(C_3H_8 + 5 O_2 \rightarrow 3 CO_2 + 4 H_2O ~~~~\Delta H_3 = -2222 kJ\)

(4) \(C_3H_8 \rightarrow 3 C + 4 H_2 ~~~\Delta H_4= 104 kJ\)


So we reverse (2), and we multiply their enthalpy change by -1

(1) \( 3 C + 3 O_2 \rightarrow 3 CO_2 ~~~~\Delta H_1 = x\)

(2) \( 4 H_2O\rightarrow4 H_2 + 2 O_2~~~~ \Delta H_2= 1144 kJ\)

(3) \(C_3H_8 + 5 O_2 \rightarrow 3 CO_2 + 4 H_2O ~~~~\Delta H_3 = -2222 kJ\)

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(4) \(C_3H_8 \rightarrow 3 C + 4 H_2 ~~~\Delta H_4= 104 kJ\)

Then we have \(\Delta H_4=\Delta H_4+\Delta H_4+\Delta H_4\)

Answer 8

i made a mistake, you are to reverse (1) not (2). the rest is fine though, do you get the concept?

Answer 9

Still working on it?

Answer 10

Don't mean to rush you or anything

Answer 11

No

Answer 12

What do you mean reverse it?

Answer 13

omg I'm so sorry my connection screwed up and I didn't see your reply

Answer 14

Reverse the equation, like A -> B to B -> A.

When you do that you reverse the sign of \(\Delta H\)

Answer 15

What is it supposed to look like once you reverse it though? I don't get it

Answer 16

Also, I'm still confused over what the answer would be. Is it B?

Answer 17

Sorry, this is too much to type out, and i have to step out. I think choice 4 is correct. I can help you solve it later if you want to, just tag me.

Answer 18

Thanks.

Answer 19

SO i double checked it and it's A. sorry about that, i can type up a solution if you're still confused.