Table of Contents
- 1 What is the standard enthalpy of formation for H2O?
- 2 Which phase change is exothermic H2O S → H2O L H2O L → H2O S H2O S → H2O g H2O L → H2O G?
- 3 Why the HF for water is identical to the standard enthalpy change of combustion of hydrogen?
- 4 Is the formation of water endothermic or exothermic?
- 5 What phase change is endothermic H2O?
- 6 Is H2O exothermic or endothermic?
- 7 During which phase change does the entropy of a sample of h20 increase?
- 8 Why is the standard enthalpy of formation of hydrogen zero?
- 9 What is the difference in enthalpy of formation between H2O and H2O?
- 10 Why is the formation of H2O as a liquid more exothermic?
What is the standard enthalpy of formation for H2O?
-285.8 kJ/mol
The standard enthalpy of formation of H2O(l) is -285.8 kJ/mol.
Which phase change is exothermic H2O S → H2O L H2O L → H2O S H2O S → H2O g H2O L → H2O G?
When solid sodium hydroxide is added to water, the temperature increases. Exothermic; there is an increase in temperature. Freezing of water to form ice is represented by the following equation. H2O(l) → H2O(s) Exothermic; energy is released when bonds are being made between water molecules in the phase change.
Why is there a change in enthalpy when water is a liquid in the products as opposed to a gas )?
They differ in enthalpy change. In the first, gaseous water is formed, and in the second, liquid water is formed; the difference between their enthalpy changes reflects the difference in energy content between a gas and a liquid.
Why the HF for water is identical to the standard enthalpy change of combustion of hydrogen?
The heat of combustion of hydrogen is the same as the enthalpy of formation ( Hf) of liquid water because it forms the molecule water from its elements (hydrogen and oxygen) in their standard states at 25 deg C (H2 and O2).
Is the formation of water endothermic or exothermic?
It is given to us that formation of water from hydrogen and oxygen gas is exothermic, which means the energy of the reactant is higher than that of the products.
Which equation would correctly represent the standard enthalpy of formation reaction for H2O L )?
H2(g)+21O2(g)→H2O(l)
What phase change is endothermic H2O?
Phases and Phase Transitions
| Phase Transition | Direction of ΔH |
|---|---|
| Vaporization (liquid to gas) | ΔH>0; enthalpy increases (endothermic process) |
| Sublimation (solid to gas) | ΔH>0; enthalpy increases (endothermic process) |
| Freezing (liquid to solid) | ΔH<0; enthalpy decreases (exothermic process) |
Is H2O exothermic or endothermic?
The reaction that forms water (from the elements it is composed of) is the combustion of hydrogen, which is clearly exothermic!
What happens when the water molecules are changing phase?
A phase change is occuring; the liquid water is changing to gaseous water, or steam. On a molecular level, the intermolecular forces between the water molecules are decreasing. When considering phase changes, the closer molecules are to one another, the stronger the intermolecular forces.
During which phase change does the entropy of a sample of h20 increase?
When a substance goes from a solid to a gas (sublimation) or from a liquid to a gas (evaporation), entropy increases. Likewise, when a solid dissolves in water, entropy increases. Entropy (i.e. the number of arrangements a system can have) is much greater in a gas than in a liquid or solid.
Why is the standard enthalpy of formation of hydrogen zero?
The enthalpy of formation of any substance can never be zero since bond formation is an exothermic process and some heat is definitely lost when H2 is formed from individual H atoms. The standard enthalpy of formation of any pure element in its naturally occurring form is taken as 0 J.
Why is stand enthalpy change of liquid water more exothermic than vapor?
Stand enthalpy change of liquid water is more exothermic than formation of water vapor because heat energy is absorbed to overcome the bonds between water molecule in the liquid state to form water in the gaseous state. so part of the heat given out is absorbed during the process.
What is the difference in enthalpy of formation between H2O and H2O?
The difference in enthalpy of formation is, of course, the enthalpy of vaporization of water. As you know from boiling water, you need energy to form water vapour from liquid water. So, standard enthalpy of formation for H2O (l) is 44 kJ/ mol more exothermic than for H2O (g).
Why is the formation of H2O as a liquid more exothermic?
Since forming the gas just takes one more step (boiling) and that takes up heat compared to forming the liquid, forming the liquid is more exothermic than forming the gas. Originally Answered: Why is the formation of H2O as a liquid more exothermic than the formation of H2O as a gas?
Is the transformation of liquid water to steam endothermic or exothermic?
In order for a reaction to be considered exothermic, it must give off enegry. This enegry is usually in the form of heat. Now, lets remind ourselves of a basic concept. At room temperature water is a liquid. To get water into a gaseous state heat must be added. Thus, the transformation of liquid water to steam is endothermic.