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+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "# Chapter 7 The second law"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Ex:7.2 Pg:192"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 1,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "Entropy in ab part = 0.1213 Btu/lbm R\n",
+      "\n",
+      " Entropy in ac part = 0.1688 Btu/lbm R\n",
+      "\n",
+      " Efficiency = 9.80 percent\n",
+      "The answers are a bit different due to rounding off error in textbook\n"
+     ]
+    }
+   ],
+   "source": [
+    "from math import log\n",
+    "#Initialization of variables\n",
+    "cv=0.175 #Btu/lbm R\n",
+    "R0=1.986\n",
+    "M=29\n",
+    "T2=1040 #R\n",
+    "T1=520 #R\n",
+    "#calculations\n",
+    "cp=cv+R0/M\n",
+    "sab=cv*log(T2/T1)\n",
+    "sac=cp*log(T2/T1)\n",
+    "dqab=cv*(T2-T1)\n",
+    "dqca=cp*(T1-T2)\n",
+    "dqrev=T2*(sac-sab)\n",
+    "eta=(dqab+dqrev+dqca)/(dqab+dqrev)\n",
+    "#results\n",
+    "print \"Entropy in ab part = %.4f Btu/lbm R\"%(sab)\n",
+    "print \"\\n Entropy in ac part = %.4f Btu/lbm R\"%(sac)\n",
+    "print \"\\n Efficiency = %.2f percent\"%(eta*100)\n",
+    "print \"The answers are a bit different due to rounding off error in textbook\""
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Ex:7.3 Pg:193"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 3,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "Change in entropy of the process = 0.0192 Btu/R\n",
+      "The answer is a bit different due to rounding off error in textbook\n"
+     ]
+    }
+   ],
+   "source": [
+    "from __future__ import division\n",
+    "from math import log\n",
+    "#Initialization of variables\n",
+    "tc=32 #F\n",
+    "th=80 #F\n",
+    "mw=5 #lbm\n",
+    "mi=1 #lbm\n",
+    "P=14.7 #psia\n",
+    "cp=1\n",
+    "#calculations\n",
+    "t= (-144*mi+tc*mi+th*mw)/(mw+mi)\n",
+    "ds1=144/(tc+460)\n",
+    "ds2=cp*log((460+t)/(460+tc))\n",
+    "dsice=ds1+ds2\n",
+    "dswater=mw*cp*log((t+460)/(460+th))\n",
+    "ds=dsice+dswater\n",
+    "#results\n",
+    "print \"Change in entropy of the process = %.4f Btu/R\"%(ds)\n",
+    "print \"The answer is a bit different due to rounding off error in textbook\""
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Ex:7.4 Pg:194"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 4,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "Change in available energy = -3.5 Btu/lbm\n",
+      "\n",
+      " The available energy of the isolated system decreased in the amount of  -36.5 Btu/lbm\n",
+      "The answer is a bit different due to rounding off error in textbook\n"
+     ]
+    }
+   ],
+   "source": [
+    "from __future__ import division\n",
+    "from math import log\n",
+    "\n",
+    "#Initialization of variables\n",
+    "cp=1\n",
+    "T2=60 #F\n",
+    "T1=100 #F\n",
+    "ta=32 #F\n",
+    "#calculations\n",
+    "dq=cp*(T2-T1)\n",
+    "ds=cp*log((460+T2)/(460+T1))\n",
+    "dE=dq-ds*(ta+460)\n",
+    "dec=dq-dE\n",
+    "#results\n",
+    "print \"Change in available energy = %.1f Btu/lbm\"%(dE)\n",
+    "print \"\\n The available energy of the isolated system decreased in the amount of  %.1f Btu/lbm\"%(dec)\n",
+    "print \"The answer is a bit different due to rounding off error in textbook\""
+   ]
+  }
+ ],
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