Calculate Δhrxn for The Following Reaction: Cs+h2ogcog+h2g

The standard enthalpy change (ΔHrxn) for a chemical reaction is a fundamental thermodynamic property that describes the heat absorbed or released during the reaction under standard conditions (25°C and 1 atm pressure). This calculator helps you determine ΔHrxn for the reaction CS + H2O → CO + H2 using standard enthalpies of formation.

How to Calculate ΔHrxn

To calculate the standard enthalpy change for the reaction CS + H2O → CO + H2, follow these steps:

Identify the standard enthalpies of formation (ΔHf°) for each compound involved in the reaction.
Calculate the total enthalpy of the reactants by summing the ΔHf° values of CS and H2O.
Calculate the total enthalpy of the products by summing the ΔHf° values of CO and H2.
Determine ΔHrxn by subtracting the total enthalpy of the reactants from the total enthalpy of the products.

The formula for ΔHrxn is:

ΔHrxn = ΣΔHf°(products) - ΣΔHf°(reactants)

Formula

The standard enthalpy change for a reaction is calculated using the standard enthalpies of formation of the products and reactants. The formula is:

ΔHrxn = [ΔHf°(CO) + ΔHf°(H2)] - [ΔHf°(CS) + ΔHf°(H2O)]

Where:

ΔHf°(CO) = Standard enthalpy of formation of carbon monoxide
ΔHf°(H2) = Standard enthalpy of formation of hydrogen gas
ΔHf°(CS) = Standard enthalpy of formation of carbon disulfide
ΔHf°(H2O) = Standard enthalpy of formation of water

Note: Standard enthalpies of formation are typically reported in units of kJ/mol. The values used in this calculation are based on standard thermodynamic data.

Example Calculation

Let's calculate ΔHrxn for the reaction CS + H2O → CO + H2 using the following standard enthalpies of formation (in kJ/mol):

ΔHf°(CO) = -110.5 kJ/mol
ΔHf°(H2) = 0 kJ/mol (by definition)
ΔHf°(CS) = -105.5 kJ/mol
ΔHf°(H2O) = -241.8 kJ/mol

Example Input

Using the standard enthalpies of formation:

ΔHrxn = [(-110.5) + 0] - [(-105.5) + (-241.8)]

Calculation:

ΔHrxn = [-110.5] - [-105.5 - 241.8] ΔHrxn = [-110.5] - [-347.3] ΔHrxn = -110.5 + 347.3 ΔHrxn = 236.8 kJ/mol

Result:

ΔHrxn = 236.8 kJ/mol

This result indicates that the reaction CS + H2O → CO + H2 is endothermic, absorbing 236.8 kJ of energy per mole of reaction.

Interpreting the Result

The calculated ΔHrxn value provides important information about the reaction:

If ΔHrxn is positive, the reaction is endothermic and absorbs heat from the surroundings.
If ΔHrxn is negative, the reaction is exothermic and releases heat to the surroundings.
The magnitude of ΔHrxn indicates the energy change per mole of reaction.

In our example, ΔHrxn = 236.8 kJ/mol indicates that the reaction requires energy input to proceed, making it endothermic.

Remember that ΔHrxn values are based on standard conditions and may vary under different temperature and pressure conditions.

FAQ

What is the standard enthalpy change (ΔHrxn)?

The standard enthalpy change (ΔHrxn) is the heat absorbed or released during a chemical reaction under standard conditions (25°C and 1 atm pressure). It's calculated using the standard enthalpies of formation of the reactants and products.

How do I find standard enthalpies of formation?

Standard enthalpies of formation can be found in thermodynamic tables, chemistry textbooks, or online databases like the NIST Chemistry WebBook or the CRC Handbook of Chemistry and Physics.

What units are used for ΔHrxn?

ΔHrxn is typically reported in kilojoules per mole (kJ/mol), which represents the energy change per mole of reaction.

Can ΔHrxn be negative?

Yes, a negative ΔHrxn indicates an exothermic reaction where heat is released to the surroundings. A positive ΔHrxn indicates an endothermic reaction where heat is absorbed from the surroundings.

How does ΔHrxn relate to reaction spontaneity?

ΔHrxn is one factor in determining reaction spontaneity, but it's not the only one. The Gibbs free energy change (ΔG) considers both enthalpy and entropy changes. A negative ΔG indicates a spontaneous reaction.