For the reaction

Al(s) + 3 HCl(aq)->AlCl3(s) +3/2 H2(g) it was observed that when 4.00g of aluminum reacted with excess HCl, exactly 30,0 kJ of heat was released. What is the delta H for this reaction?

I do not understand how to get the delta H value.

Delta H for the reaction is the heat released when 1 mol Al reacts with 3 mol HCl. You have 30 kJ from 4.00 g Al. You want to convert that to 1 mol Al.

So 30 kJ x molar mass/4.00 = ? kJ per mol.

I did 30kJ X 26.9815/4.00 = 202.36

One of the anser choices that is given is -202 kJ. Is this incorrect or did I do the calculation wrong?

No, you did it correctly. We don't know how accurately the problem maker wants or exactly what molar mass s/he used for the molar mass Al. Perhaps 27 instead of 26.98. And, too, sometimes those answers are rounded and you are expected to pick the most reasonable answer. In this case, I think the the reason is rounding. You are given 4.00 which has three significant figures so three is what we can use in the answer; therefore, your answer of 202.36 would be rounded to 202 to 3 s.f. and you would be expected to look for an answer of 202.

Ok thank you for your help!

To find the value of ΔH (delta H) for the given reaction, you need to use the concept of the heat of reaction, also known as the enthalpy change.

The equation for the reaction is:
Al(s) + 3 HCl(aq) -> AlCl3(s) + 3/2 H2(g)

Given:
Mass of aluminum (Al) = 4.00 g
Heat released (q) = -30.0 kJ (negative sign indicates heat released)

To calculate ΔH, you can use the equation:
ΔH = q / moles of limiting reactant

Step 1: Determine the moles of Al used in the reaction.
To find the moles of aluminum, you need to convert the given mass of aluminum to moles using its molar mass.
The molar mass of Al is 26.98 g/mol.

Moles of Al = Mass of Al / Molar mass of Al

Step 2: Identify the limiting reactant.
To determine the limiting reactant, you compare the moles of aluminum obtained in Step 1 with the stoichiometric ratio in the balanced equation.
From the balanced equation, we can see that the stoichiometric ratio between Al and HCl is 1:3.

If the moles of Al are greater than 1/3 of the moles of HCl, then HCl is the limiting reactant.
If the moles of Al are less than 1/3 of the moles of HCl, then Al is the limiting reactant.

Step 3: Find the moles of HCl that react.
Once you determine the limiting reactant, you can calculate the moles of HCl used in the reaction based on the stoichiometry.
From the balanced equation, it is clear that 3 moles of HCl react with 1 mole of Al.

Moles of HCl = Moles of Al × (3 moles of HCl / 1 mole of Al)

Step 4: Calculate ΔH.
Now that you have the moles of the limiting reactant from Step 2, you can calculate ΔH using the formula:
ΔH = q / moles of limiting reactant

Plug in the values into the equation to find ΔH.

Remember to consider the sign of the heat (q). Since the reaction releases heat (exothermic), the sign is negative.

This calculation will give you the value of ΔH for the given reaction.