In Macbeth, what are examples of where the reality of a situation is hidden by outward appearances in Act 1?An example is "False face must hide...

You have certainly put your finger on a key theme in this
play. From the first scene of Act I, when the witches say what could be called the motto
of the play ("Fair is foul and foul is fair"), deception and the gap between appearance
and reality is key, as this motto points towards a world where everything is not what it
actually seems. Act I contains many examples you could look at, but to me the character
to focus on is Lady Macbeth. Note how she counsels her husband in Act I scene
5:

Your face,
my Thane, is a book, where men

May read strange matters. To
beguile the time,

Look like the time; bear welcome in your
eye,

Your hand, your tongue: look like th'innocent
flower,

But be the serpent
under't.

Here she says to
Macbeth that he is too readable - others can read his intentions like a book. The final
simile captures most clearly the theme you have identified. Therefore Lady Macbeth
counsels her husband to act like an "innocent flower" that draws people in, whilst all
the time secretly being the poisonous viper that lurks beneath it waiting to jump out
and kill the prey that it attracts.

In case Macbeth didn't
get the message, Lady Macbeth provides an excellent example for us in scene 6, where she
welcomes Duncan to her home whilst at the same time knowing that he will never leave
there again:

readability="15">

All our service,

In
every point twice done, and then done double,

Were poor and
single business, to contend

Against those honours deep and
broad, wherewith

Your Majesty loads our
house...

She plays the part
of an excellent hostess, whilst secretly plotting the murder of her
guest.

Hope this helps - now re-read the first Act and look
for some more! Good luck!