Question

The reported value of the energy is sometimes positive and sometimes negative. What is the meaning of a plus or a minus in front of the energy value? Why is it important? Name one example of a process from your everyday life that requires energy and one that produces energy.

clear hand writing please.

Answer 1

When any type of reaction takes place energy in any form is either absorbed from the surrounding or released to the surrounding . The reaction in which heat energy is absorbed is called endothermic reaction . The reaction in which heat energy is lost or releaed is called exothermic reaction .

The plus sign indicates that the energy is absorbed or the reaction is endothermic in nature . Here Energy of product will be more than the energy of reactants hence ∆E is positive

The minus sign uneducated that the energy is released and the reaction is exothermic in nature . Here, The energy of the product will be less than the energy of the reactants hence ∆E will be negative

(∆E is the change is energy and given by the formula[ ∆E = E (product ) - E (reactants)] )

It is important to determine whether a reaction is endothermic or exothermic because it affects the equilibrium of the chemical reaction .

Le chateliers principle states that any outside stress such as change in temperature , pressure or concentration shifts the reaction in such a way that it re establishes the equilibrium .

Here the type of shift in equilibrium due to change in temperature is different for endothermic and exothermic reaction

For exothermic reaction the equilibrium constant value decreases with increase in temperture and equilibrium shifts to left and vice versa

For endthermic reactions the equilibrium constant value increases with increase in temperature and reaction shifts to right and vice versa .

Also , the positive and negative sign helps in calculating total energy requirement in a multiple step chemical reaction .

Hence it's is necessary to determine whether the reaction is endothermic or exothermic in nature .

Examples from daily life that requires energy is melting of ice. Ice captures heat from the surrounding and melts into water and hence requires energy and is an endothermic reaction

Examples from daily life in which energy is produces is burning of candle .

Burning of candle gives light and heat (two forms of energy) and hence here energy is produce and reaction is exothermic in nature .