evaluating expression with bash [duplicate]

There is something i do not understand with strings in bash:

Look at this script:

#!/bin/bash
tmp="ls"
"$tmp"

This script executes ls command and display result in the console.

Now look at this script:

#!/bin/bash
tmp="ls > out.txt"
"$tmp"

This second script does not execute ls and displays this error:

 line 3: ls > out.txt: command not found

I just want to understand. I do not want to understand how to run ls command. I want to understand why the first script works and not the second.

Thanks