A chemist reacts sodium hydroxide with hydrochloric acid in a glass beaker. As the reaction proceeds, the chemist observes that the glass beaker in which the reaction is taking place in feels warm. Is this an endothermic or exothermic reaction? How do you know?
It is endothermic; heat energy has been released to the surroundings, making the container warm.
It is exothermic; heat energy has been released to the surroundings, making the container warm.
It is exothermic; heat energy has been absorbed from the surroundings, making the container warm.
It is endothermic; heat energy has been absorbed from the surroundings, making the container warm.
It is exothermic; heat energy has been released to the surroundings, making the container warm.
Which type of reaction has occurred if the products have more potential energy than the reactants?
radiation
convection
endothermic
exothermic
Endothermic.
How much energy must be absorbed to break the bonds of the 2 molecules of HI?
To answer this question, we need to know the bond energy of the HI molecule. The bond energy is the amount of energy required to break a bond. The value of bond energy for HI molecule is 299 kJ/mol.
Therefore, the amount of energy required to break the bonds of 2 molecules of HI can be calculated as follows:
2 moles of HI is equal to 2 x 127 g/mol = 254 g/mol
The amount of energy required to break the bonds of 2 moles of HI is:
299 kJ/mol x 2 mol = 598 kJ
Therefore, it requires 598 kJ of energy to break the bonds of 2 molecules of HI.
How much energy is released when the bonds of H2 and I2 form in the products?
To answer this question, we need to know the bond energy of H-H bond and I-I bond, as well as the bond energy of the H-I bond that is formed.
The bond energy of H-H bond is 436 kJ/mol, and the bond energy of I-I bond is 151 kJ/mol. The bond energy of H-I bond is 299 kJ/mol.
For the reaction of H2 and I2 forming HI, the equation is:
H2 + I2 → 2HI
In this reaction, one H-H bond and one I-I bond break, while two H-I bonds are formed. Therefore, the energy change for this reaction can be calculated as follows:
Energy required to break H-H bond = 436 kJ/mol x 1 mol = 436 kJ
Energy required to break I-I bond = 151 kJ/mol x 1 mol = 151 kJ
Energy released to form two H-I bonds = 299 kJ/mol x 2 mol = 598 kJ
Total energy change for the reaction = energy required to break bonds - energy released to form bonds
= (436 kJ + 151 kJ) - (598 kJ)
= -11 kJ
The negative sign indicates that the reaction is exothermic, and 11 kJ of energy is released in the process of forming H-I bonds.
What is the total energy of the reaction?
To determine the total energy of the reaction, we need the enthalpy (or heat) of formation values for each of the reactants and products involved in the reaction. The enthalpy of formation is the energy change that takes place when one mole of a substance is formed from its constituent elements in their standard states under standard conditions (usually 25°C and 1 atm pressure).
Assuming standard conditions of 25°C and 1 atm pressure, the enthalpy of formation values for the reaction of H2 and I2 forming 2HI are:
ΔHf(H2) = 0 kJ/mol (enthalpy of formation for elemental H2 is defined as zero)
ΔHf(I2) = 0 kJ/mol (enthalpy of formation for elemental I2 is defined as zero)
ΔHf(HI) = -22.5 kJ/mol
Using Hess's Law, the total energy of the reaction can be calculated as follows:
Total energy = ∑(n * ΔHf(products)) - ∑(n * ΔHf(reactants))
where n is the number of moles of each species involved in the reaction.
Applying this formula to the reaction of H2 and I2 forming 2HI, we get:
Total energy = [2 mol (ΔHf(HI) = -22.5 kJ/mol)] - [(1 mol * 0 kJ/mol) + (1 mol * 0 kJ/mol)]
= -45 kJ/mol
So, the total energy of the reaction is -45 kJ/mol. The negative sign indicates that energy is released in the reaction, making it exothermic.