Carol E. answered • 03/21/16

Tutor

4.9
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Chemistry is my specialty!!

Hi Kaylee!

Let me help you with this.

First, let's write the balance chemical reaction for the burning of Mg:

2 Mg + O

_{2 }--> 2 MgOSecond, convert the quantity of magnesium from grams to moles:

1.20 g Mg (1mole Mg/24.3 g ) = 0.0493 mol Mg

Third, we have the calorimetry:

q = m(C

_{p})ΔT, where ΔT is always final T minus initial TThe question gives the mass of water, the C

_{p}of water is 4.184 J/g-C, and the initial T of the water is 5 C. But what about q? In the chemical equation, MgO is made from its elements, so we can use the enthalpy of formation from a thermodynamics table in a textbook. My text gives the ΔH as -601.8 kJ/mole MgO.But that quantity has to be converted to joules and is per mole of MgO. So,

601.8 kJ/mole (1000 joules/kJ)(0.0493 mole) =29669 joules

Plug in for q:

29699 joules = (500 g)(4.184 J/g-C) (T

_{f}- 5)Take it from here and solve.

I hope this was helpful. Message me if you have any questions.