Look at the graph. The orange arrow represents the summation of activation energy and reactant's initial internal energy. Can it change with temperature? Is there any specific name for this summation?
Chemistry Stack Exchange is a question and answer site for scientists, academics, teachers, and students in the field of chemistry. It only takes a minute to sign up.Sign up to join this community
No. As the label at the y-axis indicates, we are talking about potential energy. Potential energy itself does not mean anything, only energy differences can be meaningfully interpreted. (It is the same with heights, to quantify how tall a mountain is you give its height with respect to the sea level.)
The activation energy is defined as the difference between the transition state's energy and the reactant's initial internal energy, and has therefore a physical meaning. The reactant's initial internal energy itself is just some arbitrary value. Unless you define some reference point, which is not the case in your figure.
Therefore the orange arrow ("the summation of activation energy and reactant's initial internal energy") is conceptually wrong.
Furthermore, a change in temperature does not change your potential curve. This curve is a minimum energy path. It represents the ground state of the system at each point along the reaction coordinate. But when we have a ground state, then there are excited states as well. And thermal energy makes the system partially occupy these states (either statistically in the classical sense or by probability distributions in the quantum mechanical sense). Effectively the reactant will be higher in energy, but potential remains the same! This is actually the way you can reach the transition state.
Think of it like there is a ladder on the floor. The floor will be the ground state, and on the top of the ladder there is the transition state. Now the higher the temperature, the higher you can step on the ladder. With high enough temperature you can reach the transition state and descend on the other side towards the products.