I need help with these

This is due tomorrow... :How can you tell the mass was conserved in a chemical reaction?

kipiarov [429]

Answer:

Matter cannot be created or destroyed in chemical reactions. This is the law of conservation of mass. In every chemical reaction, the same mass of matter must end up in the products as started in the reactants. Balanced chemical equations show that mass is conserved in chemical reactions.

Explanation:

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3 0

3 years ago

Determine the enthalpy change for the decomposition of calcium carbonate. CaCO₃(s) --> CaO(s) + CO₂(g) given the thermochemic

Hunter-Best [27]

Answer: c. 179 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 Hess’s law, the chemical equation can be treated as algebraic expressions 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.

Given:

$Ca(OH)_2(s)\rightarrow CaO(s)+H_2O (l)$ $\Delta H_1= 65.2 kJ/mol$ (1)

$Ca(OH)_2(s)+CO_2(g)\rightarrow CaCO_3(s)+H_2O(l)$ $\Delta H_2= -113.8 kJ/mol$ (2)

$C(s)+O_2(g)\rightarrow CO_2(g)$ $\Delta H_3= -393.5 kJ/mol$ (3)

$2Ca(s)+O_2(g)\rightarrow 2CaO(s)$ $\Delta H_4=-1270.2 kJ/mol$ (4)

On subtracting eq (1) from eq (2) we have:

$Ca(OH)_2(s)\rightarrow CaO(s)+H_2O(l)$ - $Ca(OH)_2(s)+CO_2(g)\rightarrow CaCO_3(s)+H_2O(l)$

$CaCO_3(s)\rightarrow CaO(s)+CO_2(g)$

$\Delta H=-113.8-(65.2)kJ/mol=-179kJ/mol$

Hence the enthalpy change for the raection is 179.0 kJ/mol.

6 0

3 years ago

The change in enthalpy for the reaction A - P is x kJ/mol. What does the enthalpy change for the reaction P -A? (A) -x kJ/mol (B

nikdorinn [45]

Answer : The correct option is, (A) -x 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 chemical reaction is,

$A\rightarrow P$ $\Delta H=x\text{ kJ/mole}$