The hydrogen bond is a secondary bond formed between a hydrogen (attached to an highly electronegative element ,: F, O or N) and another atom of an highly electronegative element ,: F, O or N.
In case of water hydrogen bond helps water
a) to dissolve certain substances which can make hydrogen bond
b) it makes it liquid and room temperature unlike H2S which is a gas at room temperature due to absence of hydrogen bond
c) higher volume and low density of ice as compared to liquid water. Due to hydrogen bond ice forms open cage like structure which increases its volume and decreases its density. Thus water expands on freezing
So in absence of hydrogen bond Water would not expand when it freezes.
chemical reactions?
The mass of the reaction system is conserved because, the mass lost from the reaction by the evolution of gas is collected inside a balloon to inflate it. Thus , the balloon and the flask creates a closed system where no mass is lost outside.
According to the law of conservation of mass, the mass can neither be created nor be destroyed. Thus the total mass of the system is conserved. However similar to the energy, mass can be transformed into energy.
As per this law, the total mass in a chemical reaction is conserved. Where, the total mass in the reactant side is equal to the total mass in the product side.
When the reaction flask is closed with a balloon, the gas if any evolved from the reaction will be collected to the balloon and it inflates. Thus the mass lost from the reaction system does not goes to the surroundings due to the closed system.
To find more on mass conservation, refer here:
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True
As the shorter the bond, the stronger it is hence more energy will be required to overcome this bond
The statement 'The longer the bond, the smaller the bond enthalpy' is true as bond length and bond enthalpy have an inverse relationship. As bond strength increases (with an increase in electron pairs in the bond), bond length decreases. So longer bonds, indicating weaker bonding, have smaller bond enthalpies.
The statement 'The longer the bond, the smaller the bond enthalpy' is true. The bond length and bond enthalpy have an inverse relationship. As the strength of a bond increases with the increase in the number of electron pairs, the bond length decreases. Thus, triple bonds are generally stronger and shorter than double bonds between the same two atoms, and by the same logic, double bonds are stronger and shorter than single bonds.
For example, if we consider the bonds between carbon and various atoms in a group, we find the bond strength typically decreases as we move down the group - C-F has a bond enthalpy of 439 kJ/mol, C-Cl has 330 kJ/mol, and C-Br is at 275 kJ/mol.
The bond energy, essentially the enthalpy required to break the bond, is a representation of its strength. Thus, a longer bond, indicating weaker bonding, will have a smaller bond enthalpy.
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