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4 years ago

Calcium carbide (CaC2) reacts with water to form acetylene (C2H2) and Ca(OH)2.

1 answer:

4 0

The answer is -60.57. With appropriate sig figs it becomes -60.6 KJ.

I think you were on the right track. However you need to multiply H2O by its coefficient from the balanced equation. Then you also need to keep in mind the signs. 

Maybe it's easier if I write what I did out: 

2H2O > 2H2 +O2...............-H= 2* -285.83 
Ca + O2 + H2 > Ca(OH)2....H= -986.2 
2C + H2 > C2H2.................H= 226.77 

The above H's stand for standard enthalpy of formations. These can be found in textbook appendix. Notice the negative infront of the enthalpy (H) for H2O. This is to remind me/you that the heat lost is gained in the rxn. 

So then you add them up. 226.77 - 986.2 + (2*285.83) = -187.77 

Add back the total enthalpy that is given in the question -187.77+127.2 = -60.57 

If signs cross you up find a way to remember that works for you.

You might be interested in

What mass of hydrogen sulfide, H2S, will completely react with 2.00 moles of silver nitrate, AgNO3?

hodyreva [135]

Answer:

34g

Explanation:

We'll begin by writing the balanced equation for the reaction. This is illustrated below:

H2S + 2AgNO3 —> 2HNO3 + Ag2S

Next, we shall determine the number of mole of H2S required to react with 2 moles of AgNO3.

This is illustrated below:

From the balanced equation above,

We can see that 1 mole of H2S is required to react completely with 2 moles of AgNO3.

Finally, we shall convert 1 mole of H2S to grams. This is shown below:

Number of mole H2S = 1 mole

Molar mass of H2S = (2x1) + 32 = 34g/mol

Mass = number of mole x molar Mass

Mass of H2S = 1 x 34

Mass of H2S = 34g

Therefore, 34g of H2S is needed to react with 2 moles of AgNO3.

6 0

3 years ago

All the substances listed below are fertilizers that contribute nitrogen to the soil.

kvv77 [185]

Answer:

Ammonia is the richest source of nitrogen on a mass percentage basis because it has 82.35% of nitrogen by mass.

Explanation:

Percentage of element in compound :

$=\frac{\text{number of atoms}\times text{Atomic mass}}{\text{molar mas of compound}}\times 100$

(a) Urea, $(NH_2)_2CO$

Molar mass of urea = 60 g/mol

Atomic mass of nitrogen = 14 g/mol

Number of nitrogen atoms = 2

$N\%=\frac{2\times 14 g/mol}{60 g/mol}\times 100=46.67\%$

(b) Ammonium nitrate, $NH_4NO_3$

Molar mass of ammonium nitrate = 80 g/mol

Atomic mass of nitrogen = 14 g/mol

Number of nitrogen atoms = 2

$N\%=\frac{2\times 14 g/mol}{80 g/mol}\times 100=35.00\%$

(c) Nitric oxide, NO

Molar mass of nitric oxide = 30 g/mol

Atomic mass of nitrogen = 14 g/mol

Number of nitrogen atoms = 1

$N\%=\frac{1\times 14 g/mol}{30 g/mol}\times 100=46.67\%$

(d) Ammonia, $NH_3$

Molar mass of ammona = 17 g/mol

Atomic mass of nitrogen = 14 g/mol

Number of nitrogen atoms = 1

$N\%=\frac{1\times 14 g/mol}{17 g/mol}\times 100=82.35\%$

Ammonia is the richest source of nitrogen on a mass percentage basis because it has 82.35% of nitrogen by mass.

4 0

3 years ago

2.38g of black copper(iii) oxide is completely reduced to by hydrogen to give copper and water. What are the number of atoms of

OleMash [197]

Explanation:

here is the answer bae. Feel free to ask for more

6 0

3 years ago

3. Given the following equation:

miskamm [114]

Answer:

4.767 grams of KCl are produced from 2.50 g of K and excess Cl2

Explanation:

The balanced equation is

2 K+ Cl2 --->2 KCI

Here the limiting agent is K. Hence, the amount of KCl will be calculated as per the mass of 2.50 gram of K

Mass of one atom/mole of potassium is 39.098 grams

Number of moles is 2.5 grams = $\frac{2.5}{39.098} = 0.064$

So, 2 moles of K produces 2 moles of KCL

0.064 moles of K will produces 0.064 moles of KCl

Mass of one molecule of KCl is 74.5513 g/mol

Mass of 0.064 moles of KCl is 4.767 grams

4 0

3 years ago

Which compounds are classified as electrolytes and why?

djyliett [7]

The correct answer is A. An electrolyte is a substance that conducts electricity in solution because the solution has ions that electricity can flow. KNO3 and H2SO4 dissociates into potassium, nitrate, hydronium and sulfate ions when in solution therefore they are considered as electrolytes.

6 0

4 years ago