So I am writing a lab report and Im stuck with calculating the enthalpy change of combustion of the following reaction:
Mg+2HCl--> MgCl2+H2 .I am given the mass of Mg which is 5g and the concentration of HCl which is 2M and the volume of HCl which is 50 cm^3.I found the limiting reactant which was HCl and i have to measure the ÄÇ of combustion..I know that HE(HEAT ENERGY)=m x c x ÄT and the change in temperature is 10 degrees celsius. I also know that in order to find ÄH we divide HE with n which is the number of moles of the limiting reactant..can anyone please help me find the ÄH?i DON'T know whose mass to use, i know i have to use the heat capacity of water..and i don't know whether i have to convert temperature into Kelvin measurement.
Frankly, I don't know how you are to calculate heat of combustion when you didn't combust Mg but reacted it with HCl instead.
You measured the T difference of the water; therefore, find the q from mc*delta T by using the mass of water (50 cc = 50g if the density is 1.00 g/cc) and the specific heat of water.
we were asked to find the enthalpy change because it is an exothermic reaction. Don't i have to convert cm^3 into dm^3 in the equation?when i divide the Heat energy with the number of moles in order to get enthalpy change do i put the moles of the limiting reagent?
You want the mass of the water and the volume of the water is 50 cc. Since the density is 1.00 g/cc, the mass is 50 g. You CAN convert cc to dm^3 if you want to use a different value for density in g/dm^3. After finding q, then delta H rxn = q/n for the limiting reagent which gives J/mol for the unit.
To calculate the enthalpy change of combustion (ΔH) for the reaction Mg + 2HCl → MgCl2 + H2, you will need to follow these steps:
1. Determine the limiting reactant:
- Calculate the number of moles of Mg using its molar mass (24.31 g/mol) and the given mass of Mg (5 g).
- Calculate the number of moles of HCl using its concentration (2 M) and volume (50 cm^3 converted to liters).
- Compare the ratios of moles between Mg and HCl in the balanced chemical equation to identify the limiting reactant.
2. Calculate the heat energy (HE):
- Use the equation: HE = m × c × ΔT, where m is the mass of the limiting reactant, c is the specific heat capacity of water (4.18 J/g·°C), and ΔT is the change in temperature.
3. Calculate the number of moles of the limiting reactant:
- Divide the mass of the limiting reactant by its molar mass.
4. Calculate the enthalpy change of combustion (ΔH):
- Divide the heat energy (HE) by the number of moles of the limiting reactant (n).
Regarding your other questions:
- Use the mass of the limiting reactant when calculating the heat energy (HE) because it is the reactant that determines how much heat is released.
- You should convert the temperature to Kelvin (K) because Kelvin is the absolute temperature scale. To convert from Celsius to Kelvin, add 273.15 to the Celsius temperature.
By following these steps and using the appropriate values, you should be able to calculate the enthalpy change (ΔH) of the combustion reaction.