If 6g of pure carbon is completely burned

[naren11]

Ques: If 6g of pure carbon is completely burned, what mass of carbon must be burned to furnish 39.3 kj of heat?

For this ques, the equation would be $$C + O_2 \xrightarrow~ C O_2$$


well, iam stuck after this

 

[mrjeffy321]

well, we know that any reactant and product in its natural state has an enthalpy of zero.
Carbon, and Oxygen gas both are zero,
carbon dioxide has an enthalpy of -393.51 kJ/mol,
so the differenc of enthalpy of the products to the reactants is -393.51 kJ for every 1 mol of carbhon dioxide formed.so now figure out how many moles need to be formed to make 39.3 kJ, and then work backward to get the mols of carbon needed, then from that you can get the mass of the carbon needed.

 

[naren11]

how did u get the enthalpy of carbon, -393.51 kJ/mol, ?

 

[mrjeffy321]

I looked it up in a chart I have.
Many textbooks have charts with values of enthalpy, entropy, and free energy for common elements, usually located in the back appendixes or in the chapters pretaining to these values.
You can also find many more complete charts online.