Edit in JSFiddle

(function($) {
    $('div').hover(function() {
        $(this).animate({width: 200}, 1000);
    }, function() {
        $(this).animate({width: 100}, 1000);
    });
})(jQuery);

<div>Hello there!</div>

div {
    width: 100px;
    height: 100px;
    background: red;
}