What is the impact of poetic devices used in "IF" by Rudyard Kipling?

1) Personification is when inanimate objects are spoken about as if they were human.  For example, the following sentence uses personification: The sun was smiling on the children in the park.

"If" is not very rich in personification.  The only example I can find is:

And so hold on when there is nothing in you
Except the Will which says to them: "Hold on";

In this passage, a person's "will" is pictured as a living being that can "talk" and say, "Hold on." 

2) Alliteration is the repetition of beginning consonant sounds.  Some examples from "If" are:

"treat those two impostors";
"the truth you've spoken/Twisted by knaves to make a trap for fools";
"sinew/To serve your turn.../And so hold on..."

These examples of alliteration, and others, serve to draw the reader's attention to certain key phrases.  In the second passage, for example, alliteration draws our attention to some of the opposing forces that the poem discusses: truth, and traps.

3) Metaphors are comparisons that do not use the words "like" or "as."  This poem speaks mostly in straightforward language; still, it does contain some metaphors, such as:

"triumph and disaster...those two impostors"';
"the truth.../Twisted by knaves to make a trap for fools" (truth is compared to a metal object that can be twisted out of shape).

Metaphors such as these make the poem much more beautiful and memorable.  Imagine if Kipling had written: If you can bear to hear the truth you've spoken misrepresented by knaves in such a way that they would cause fools to make intellectual errors.  Not exactly memorable!

4) By far the most important device used in this poem is the repetition of similar words or phrases; this is referred to as anaphora. 

Consider these examples  just from the first stanza:

when all men DOUBT you,/But make allowance for their DOUBTING;
If you can WAIT and not be tired by WAITING;
Or, being LIED about, don't deal in LIES;
Or, being HATED, don't give way to HATING.

These repetitions serve to emphasis one of the poem's major themes: balance.  Kipling believes that many character traits and actions must be used, but always in the proper balance.

You must wait sometimes, but not become worn out by waiting. You must be decisive, but not so cocksure that you cannot "make allowance" for others who doubt.  You must dream, but not be enslaved to your dreams; you must think, but "not make thoughts your aim."

Kipling uses several devices effectively to draw the attention of the reader and make us think.

First in these lines:

If you can meet with triumph and disaster
And treat those two imposters just the same;

he personifies triumph and disaster by giving them the abilities to be imposters. Imposters are humans who distract or get involved in something we don't want them to. They could even be disguised humans. Thus, his point here is to look at both success and loss as elements in life that do the same thing for us: teach us lessons.

In terms of poetic style, it seems to have an ababcdcd rhyme scheme and Kipling has gone to great effort to put the poem in iambic pentameter.

Kipling uses word play or repetition or parallel structure in the lines:

If you can dream - and not make dreams your master;
If you can think - and not make thoughts your aim;

to play with the purposes of thoughts and dreams. You obviously see the repetition of words, but to see these same grammatical structures mean that parallel structure or parallelism is at work.

Kipling captializes the word "Will" in the 3rd stanza at the end. I believe this is a biblical allusion to God's will. When authors capitalize a word, they are often personifying. Given the era, another possibility is that this author is encouraging his son to invoke God's Will. This would make sense because the stanza is about the points in life at which we sort of lose our grip on a given situation.

The simple repetition of so many "if" statements that never reach their "then" until the very end makes the end suspenseful. The list given from the father to the son is tremendously difficult. But the prize of being a true Man is worth it. The riches and material items of the world mean nothing compared to the character that is produced.

Hope this helps.

How did Kipling convey emotion in "If" using poetic or literary devices?

In Rudyard Kipling's poem, "If," the first literary device employed that immediately draws the readers attention is repetition. Obviously, repetition occurs when a word or phrase is used over and over again. However, it is not used casually on the poet's part, but for a specific purpose. It is referred to as didactic—"a work meant to give instruction." Furthermore...

The placement of the...poem...in the collection [Rewards and Fairies] serves to distill a specific lesson from the story for its young readers.

Knowing instruction is the poem's intent, we can also find the purpose of the device as described here:

Repetition is an effective literary device that may bring comfort, suggest order, or add special meaning to a piece of literature.

In this case, I would suggest that there are two things the repetition of "If" brings to the poem. The first is a sense of "hope." The word represents the potential for dramatic things to occur, including self-control, confidence in oneself ("courage"), honesty, open-mindedness, patience, personal integrity, and grace. These are many of the rewards described just in the first stanza of the poem.

If you can keep your head when all about you

Are losing theirs and blaming it on you;

If you can trust yourself when all men doubt you,

But make allowance for their doubting too:

If you can wait and not be tired by waiting,

Or, being lied about, don't deal in lies,

Or being hated don't give way to hating,

And yet don't look too good, nor talk too wise
To take the advice given seems to promise a reward...

The poem (we find at the end) is directed to the speaker's son—and the hope is that "if" he can follow his father's suggestions, he will be rewarded in the most meaningful ways a boy (and his parent/s) could wish for: 

Yours is the Earth and everything that's in it,

And---which is more---you'll be a Man, my son!

"If" the son can do all of these things, the world can be his, but more importantly, he will be a man. This does not refer to attaining a specific number of years (e.g., 21), but rather it infers (especially in that "Man" is capitalized) that the youngster will be a person of value, and one to be admired and respected by others, as well as himself—he can well be not prideful, but proud of his achievements.

The second aspect of the repetition of "If" is the sense that being used so many times, it also infers a wealth of opportunities to achieve this distinguished state of manhood. Potential, symbolized by use of "If," is seemingly endless. I would think the poet might mean that failing once does not make one a failure...if he (or she) continues to try.