Answer : The enthalpy change for the decomposition of calcium carbonate is, 178.1 kJ/mol
Explanation :
According to Hess’s law of constant heat summation, the heat absorbed or evolved in a given chemical equation is the same whether the process occurs in one step or several steps.
According to this law, the chemical equation can be treated as ordinary algebraic expression and can be added or subtracted to yield the required equation. That means the enthalpy change of the overall reaction is the sum of the enthalpy changes of the intermediate reactions.
The given main reaction is,
The intermediate balanced chemical reaction will be,
(1) 
(2) 
(3) 
(4) 
Now we are reversing reaction 1 and then adding reaction 1 and 2, we get :
(1)
(2) 
The expression for enthalpy of change will be,
Thus, the enthalpy change for the decomposition of calcium carbonate is, 178.1 kJ/mol
Answer:
hi!
Explanation:
The Mohs Hardness Scale ranks the order of hardness of minerals and some common objects. For example, your fingernail can scratch the minerals talc and gypsum, with a hardness of 2 or lower. A copper penny can scratch calcite, gypsum, and talc.
One of the most important tests for identifying mineral specimens is the Mohs Hardness Test.
This test compares the resistance of a mineral to being scratched by ten reference minerals known as the Mohs Hardness Scale (see table at left).
The test is useful because most specimens of a given mineral are very close to the same hardness. This makes hardness a reliable diagnostic property for most minerals.
"Hardness" is the resistance of a material to being scratched. The test is conducted by placing a sharp point of one specimen on an unmarked surface of another specimen and attempting to produce a scratch.
Answer:
Mass = 8 g
Explanation:
Given data:
Mass of MgO formed = 20 g
Mass of oxygen needed = ?
Solution:
Chemical equation:
2Mg + O₂ → 2MgO
Number of moles of MgO:
Number of moles = mass/molar mass
Number of moles = 20 g/ 40 g/mol
Number of moles = 0.5 mol
Now we will compare the moles of MgO and O₂ from balance chemical equation:
MgO : O₂
2 : 1
0.5 : 1/2×0.5 = 0.25 mol
Mass of oxygen required:
Mass = number of moles × molar mass
Molar mass of O₂ is 32 g/mol
Mass = 0.25 mol × 32 g/mol
Mass = 8 g
